Ruben Y. Luo, PhD, DABCC, FADLM is an Assistant Professor of Pathology at Stanford University and Associate Director of Clinical Chemistry Laboratory at Stanford Health Care. He has been dedicated to innovations in translational laboratory medicine: discovery of novel diagnostic markers and innovation of diagnostic technologies. His research focuses on (1) discovering the clinical diagnostic value of molecular characteristics of protein biomarkers, and (2) developing high-resolution mass spectrometry and label-free optical sensing technologies for characterization and accurate measurement of biomarkers. He completed his clinical chemistry fellowship at University of California San Francisco. Prior to the fellowship, he had several years of work experience in the clinical diagnostic industry. He received his PhD in analytical chemistry from Stanford University, and BS in chemistry from Peking University.

Academic Appointments

Administrative Appointments

  • Associate Director, Clinical Chemistry Laboratory, Stanford Health Care (2021 - Present)

Honors & Awards

  • AACC George Grannis Award for Excellence in Research and Scientific Publication, American Association for Clinical Chemistry (2022)
  • MSACL Lab Director Educational Grant, Mass Spectrometry & Advances in the Clinical Lab (2022)
  • NACCCA Outstanding Research Award, North American Chinese Clinical Chemists Association (2021)
  • ASCP “40 Under Forty” Honoree, American Society for Clinical Pathology (2020)
  • AACC Academy’s Distinguished Abstract Award, American Association for Clinical Chemistry (2020)
  • AACC Best Abstract Award for Outstanding Research in TDM, American Association for Clinical Chemistry (2020)
  • AACC Best Abstract Award for Outstanding Research in TDM, American Association for Clinical Chemistry (2019)
  • MSACL Young Investigator Educational Grants, Mass Spectrometry & Advances in the Clinical Lab (2018-2020)

Boards, Advisory Committees, Professional Organizations

  • Member-at-Large, Mass Spectrometry and Separation Sciences Division, American Association for Clinical Chemistry (2021 - Present)
  • Member, American Society for Clinical Pathology (2020 - 2022)
  • Board Member, North American Chinese Clinical Chemists Association (2019 - Present)
  • Member, American Society for Mass Spectrometry (2018 - Present)
  • Member, American Association for Clinical Chemistry (2017 - Present)

Professional Education

  • Board Certification, American Board of Clinical Chemistry (2020)
  • Fellowship, UCSF Clinical Chemistry Fellowship Program (2020)
  • PhD, Stanford University (2008)
  • BS, Peking University (2003)


  • R. N. Zare, Y. Luo, F. Yu. "United States Patent 8,289,519 Surface Plasmon Resonance (SPR) Microscopy Systems, Method of Fabrication Thereof, and Methods of Use Thereof", Stanford University, Oct 16, 2012

Current Research and Scholarly Interests

Apply top-down mass spectrometry and label-free immunoassay to the study and utilization of biomarker proteoforms in clinical diagnosis.


  • Application of Proteoforms in Blood and Cerebrospinal Fluid as Potential Clinical Diagnostic Markers


    Stanford, CA, USA

  • Study of β2-Transferrin and Development of a Next-Generation Assay to Detect Cerebrospinal Fluid Leak


    Stanford, CA, USA

  • Top-Down Identification of Hemoglobin Variants Using Capillary Electrophoresis Coupled with High-Resolution Mass Spectrometry


    Stanford, CA, USA

  • Development of a Therapeutic Drug Monitoring Assay for Immunosuppressive Drugs Using High-Resolution Mass Spectrometry


    Stanford, CA, USA

  • Development of a Therapeutic Drug Monitoring Assay for Antifungal Agents Using High-Resolution Mass Spectrometry


    Stanford, CA, USA

Stanford Advisees

All Publications

  • Study of β1-transferrin and β2-transferrin using microprobe-capture in-emitter elution and high-resolution mass spectrometry. Scientific reports Luo, R. Y., Pfaffroth, C., Yang, S., Hoang, K., Yeung, P. S., Zehnder, J. L., Shi, R. Z. 2023; 13 (1): 14974


    Cerebrospinal fluid (CSF) leak can be diagnosed in clinical laboratories by detecting a diagnostic marker β2-transferrin (β2-Tf) in secretion samples. β2-Tf and the typical transferrin (Tf) proteoform in serum, β1-transferrin (β1-Tf), are Tf glycoforms. An innovative affinity capture technique for sample preparation, called microprobe-capture in-emitter elution (MPIE), was incorporated with high-resolution mass spectrometry (HR-MS) to study the Tf glycoforms and the primary structures of β1-Tf and β2-Tf. To implement MPIE, an analyte is first captured on the surface of a microprobe, and subsequently eluted from the microprobe inside an electrospray emitter. The capture process is monitored in real-time via next-generation biolayer interferometry (BLI). When electrospray is established from the emitter to a mass spectrometer, the analyte is immediately ionized via electrospray ionization (ESI) for HR-MS analysis. Serum, CSF, and secretion samples were analyzed using MPIE-ESI-MS. Based on the MPIE-ESI-MS results, the primary structures of β1-Tf and β2-Tf were elucidated. As Tf glycoforms, β1-Tf and β2-Tf share the amino acid sequence but contain varying N-glycans: (1) β1-Tf, the major serum-type Tf, has two G2S2 N-glycans on Asn413 and Asn611; and (2) β2-Tf, the major brain-type Tf, has an M5 N-glycan on Asn413 and a G0FB N-glycan on Asn611. The resolving power of the innovative MPIE-ESI-MS method was demonstrated in the study of β2-Tf as well as β1-Tf. Knowing the N-glycan structures on β2-Tf allows for the design of more novel test methods for β2-Tf in the future.

    View details for DOI 10.1038/s41598-023-42064-7

    View details for PubMedID 37696850

    View details for PubMedCentralID 345148

  • Microprobe-Capture In-Emitter Elution: An Affinity Capture Technique to Directly Couple a Label-Free Optical Sensing Technology with Mass Spectrometry for Protein Analysis. Analytical chemistry Luo, R. Y., Yang, S. 2023


    Affinity capture of an analyte by a capture agent is one of the most effective sample preparation approaches in mass spectrometry (MS), especially top-down MS. We describe a new affinity capture technique for protein targets, called microprobe-capture in-emitter elution (MPIE), which can directly couple a label-free optical sensing technology (next-generation biolayer interferometry, BLI) with MS. To implement MPIE, an analyte is first captured on the surface of a microprobe and subsequently eluted from the microprobe inside an electrospray emitter. The capture process is monitored in real-time via BLI. When electrospray is established from the emitter to a mass spectrometer, the analyte is immediately ionized via electrospray ionization (ESI) for MS analysis. By this means, BLI and MS are directly coupled in the form of MPIE-ESI-MS. The performance of MPIE-ESI-MS was demonstrated by the analysis of β-amyloid 1-40 and transferrin using both standard samples and human specimens. In comparison to conventional affinity capture techniques such as bead-based immunoprecipitation, MPIE innovates the affinity capture methodology by introducing real-time process monitoring and providing binding characteristics of analytes, offering more information-rich experiment results. Thus, MPIE is a valuable addition to the top-down MS sample preparation toolbox, and MPIE-ESI-MS can be useful for identification and characterization of targets of interest.

    View details for DOI 10.1021/acs.analchem.2c04727

    View details for PubMedID 36952522

  • Neutral-Coating Capillary Electrophoresis Coupled with High-Resolution Mass Spectrometry for Top-Down Identification of Hemoglobin Variants. Clinical chemistry Luo, R. Y., Wong, C., Xia, J. Q., Glader, B. E., Shi, R., Zehnder, J. L. 2022


    BACKGROUND: Identification of hemoglobin (Hb) variants is of significant value in the clinical diagnosis of hemoglobinopathy. However, conventional methods for identification of Hb variants in clinical laboratories can be inadequate due to the lack of structural characterization. We describe the use of neutral-coating capillary electrophoresis coupled with high-resolution mass spectrometry (CE-HR-MS) to achieve high-performance top-down identification of Hb variants.METHODS: An Orbitrap Q-Exactive Plus mass spectrometer was coupled with an ECE-001 capillary electrophoresis (Ce) unit through an EMASS-II ion source. A PS1 neutral-coating capillary was used for CE. Samples of red blood cells were lysed in water and diluted in 10 mM ammonium formate buffer for analysis. Deconvolution of raw mass spectrometry data was carried out to merge multiple charge states and isotopic peaks of an analyte to obtain its monoisotopic mass.RESULTS: The neutral-coating CE could baseline separate individual Hb subunits dissociated from intact Hb forms, and the HR-MS could achieve both intact-protein analysis and top-down analysis of analytes. A number of patient samples that contain Hb subunit variants were analyzed, and the variants were successfully identified using the CE-HR-MS method.CONCLUSIONS: The CE-HR-MS method has been demonstrated as a useful tool for top-down identification of Hb variants. With the ability to characterize the primary structures of Hb subunits, the CE-HR-MS method has significant advantages to complement or partially replace the conventional methods for the identification of Hb variants.

    View details for DOI 10.1093/clinchem/hvac171

    View details for PubMedID 36308334

  • A SARS-CoV-2 Label-Free Surrogate Virus Neutralization Test and a Longitudinal Study of Antibody Characteristics in COVID-19 Patients. Journal of clinical microbiology Luo, Y. R., Yun, C., Chakraborty, I., Wu, A. H., Lynch, K. L. 2021; 59 (7): e0019321


    Methods designed to measure severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) humoral response include virus neutralization tests to determine antibody neutralization activity. For ease of use and universal applicability, surrogate virus neutralization tests (sVNTs) based on antibody-mediated blockage of molecular interactions have been proposed. A surrogate virus neutralization test was established on a label-free immunoassay platform (LF-sVNT). The LF-sVNT analyzes the binding ability of SARS-CoV-2 spike protein receptor-binding domain (RBD) to angiotensin-converting enzyme 2 (ACE2) after neutralizing RBD with antibodies in serum. The LF-sVNT neutralizing antibody titers (50% inhibitory concentration [IC50]) were determined from serum samples (n = 246) from coronavirus disease 2019 (COVID-19) patients (n = 113), as well as the IgG concentrations and the IgG avidity indices. Although there was variability in the kinetics of the IgG concentrations and neutralizing antibody titers between individuals, there was an initial rise, plateau, and then in some cases a gradual decline at later time points after 40 days after symptom onset. The IgG avidity indices, in the same cases, plateaued after an initial rise and did not show a decline. The LF-sVNT can be a valuable tool in research and clinical laboratories for the assessment of the presence of neutralizing antibodies to COVID-19. This study is the first to provide longitudinal neutralizing antibody titers beyond 200 days post-symptom onset. Despite the decline of IgG concentration and neutralizing antibody titer, IgG avidity index increases, reaches a plateau, and then remains constant up to 8 months postinfection. The decline of antibody neutralization activity can be attributed to the reduction in antibody quantity rather than the deterioration of antibody quality, as measured by antibody avidity.

    View details for DOI 10.1128/JCM.00193-21

    View details for PubMedID 33827900

  • Development of Label-Free Immunoassays as Novel Solutions for the Measurement of Monoclonal Antibody Drugs and Antidrug Antibodies CLINICAL CHEMISTRY Luo, Y., Chakraborty, I., Lazar-Molnar, E., Wu, A. B., Lynch, K. L. 2020; 66 (10): 1319-1328


    Immunoassays based on label-free technologies (label-free immunoassay [LFIA]) offer an innovative approach to clinical diagnostics and demonstrate great promise for therapeutic drug monitoring (TDM) of monoclonal antibody (mAb) drugs. An LFIA measures immunocomplex formation in real time and allows for quantification on initial binding rate, which facilitates fast measurement within a few minutes.Based on thin-film interferometry (TFI) technology, open-access LFIAs were developed for the quantification of the mAb drugs adalimumab (ADL) and infliximab (IFX) and for the detection of the antidrug antibodies (ADAs) to the mAb drugs (ADL-ADAs and IFX-ADAs).The LFIAs for active mAb drugs (ADL and IFX) and for ADAs (ADL-ADAs and IFX-ADAs) were validated. The analytical measurement range (AMR) for both ADL and IFX was from 2 to 100 μg/mL. The AMR for ADL-ADAs was from 5 to 100 μg/mL and for IFX-ADAs was 10 to 100 μg/mL. In the comparison of LFIAs and reporter gene assays, the correlation coefficient was 0.972 for the quantification of ADL and 0.940 for the quantification of IFX. The concordance rate was 90% for the detection of ADL-ADAs and 76% for the detection of IFX-ADAs.The LFIAs for active mAb drugs and ADAs were appropriate for the TDM of ADL and IFX. The TFI technology has unique advantages compared with other technologies used for the measurement of mAb drugs. Label-free technologies, especially those allowing for open-access LFIAs, have great potential for clinical diagnostics.

    View details for DOI 10.1093/clinchem/hvaa179

    View details for Web of Science ID 000582196800012

    View details for PubMedID 32918468

  • Kinetics of SARS-CoV-2 Antibody Avidity Maturation and Association with Disease Severity. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America Luo, Y. R., Chakraborty, I., Yun, C., Wu, A. H., Lynch, K. L. 2020


    The kinetics of IgG avidity maturation during SARS-CoV-2 infection was studied. The IgG avidity assay used a novel label-free immunoassay technology. It was found that there was a strong correlation between IgG avidity and days since symptom onset, and peak readings were significantly higher in severe than mild disease cases.

    View details for DOI 10.1093/cid/ciaa1389

    View details for PubMedID 32927483

    View details for PubMedCentralID PMC7543300

  • An up-conversion fluorescence lateral-flow immunoassay for rapid detection of Daratumumab in serum protein electrophoresis clinical samples. Clinica chimica acta; international journal of clinical chemistry Liu, Y., Tao, Y., Yeung, P. S., Lu, M., Liu, J., Yu, F., Shi, R., Yiqi Luo, R. 2024: 119677


    BACKGROUND: Daratumumab (DARA) is a commonly used monoclonal antibody (mAb) drug for the treatment of multiple myeloma (MM). Its appearance as a visible abnormal band in the gamma-region of a serum protein electrophoresis (SPEP) gel may interfere with the SPEP result interpretation. With the advantages of portability and rapid testing capabilities, up-conversion fluorescence lateral-flow immunoassay (LFA) can be an ideal solution to detect DARA interference.METHODS: An up-conversion fluorescence LFA strip was designed and constructed to perform semi-quantitative DARA testing in clinical samples. The LFA strip test was evaluated for limit of detection (LOD), dynamic range, and analytical interference.RESULTS: To demonstrate the clinical utility of the LFA strip, 43 SPEP-positive patient serum samples were tested for the presence of DARA, and the results exactly matched the DARA usage history in patient medical records.CONCLUSIONS: The performance of the up-conversion fluorescence LFA strip meets the purpose of clarifying DARA interference in SPEP results. It may be used as an independent and objective confirmation of the presence of DARA in clinical samples. The LFA strip offers a cost-effective rapid on-site test to check for DARA interference alongside standard SPEP equipment, which significantly improves the interpretation of ambiguous SPEP results involving DARA, and does not intervene the current SPEP workflow in clinical laboratory practice.

    View details for DOI 10.1016/j.cca.2024.119677

    View details for PubMedID 38636694

  • Transport of Full-Length Proteins through a Nanopore: One Step Closer to Single-Molecule Proteomics. Clinical chemistry Yeung, P. S., Luo, R. Y. 2024; 70 (2): 462-463

    View details for DOI 10.1093/clinchem/hvad201

    View details for PubMedID 38321876

  • Global metabolomics revealed deviations from the metabolic aging clock in colorectal cancer patients. Theranostics Zhang, L., Mo, S., Zhu, X., Chou, C. J., Jin, B., Han, Z., Schilling, J., Liao, W., Thyparambil, S., Luo, R. Y., Whitin, J. C., Tian, L., Nagpal, S., Ceresnak, S. R., Cohen, H. J., McElhinney, D. B., Sylvester, K. G., Gong, Y., Fu, C., Ling, X. B., Peng, J. 2024; 14 (4): 1602-1614


    Background: Markers of aging hold promise in the context of colorectal cancer (CRC) care. Utilizing high-resolution metabolomic profiling, we can unveil distinctive age-related patterns that have the potential to predict early CRC development. Our study aims to unearth a panel of aging markers and delve into the metabolomic alterations associated with aging and CRC. Methods: We assembled a serum cohort comprising 5,649 individuals, consisting of 3,002 healthy volunteers, 715 patients diagnosed with colorectal advanced precancerous lesions (APL), and 1,932 CRC patients, to perform a comprehensive metabolomic analysis. Results: We successfully identified unique age-associated patterns across 42 metabolic pathways. Moreover, we established a metabolic aging clock, comprising 9 key metabolites, using an elastic net regularized regression model that accurately estimates chronological age. Notably, we observed significant chronological disparities among the healthy population, APL patients, and CRC patients. By combining the analysis of circulative carcinoembryonic antigen levels with the categorization of individuals into the "hypo" metabolic aging subgroup, our blood test demonstrates the ability to detect APL and CRC with positive predictive values of 68.4% (64.3%, 72.2%) and 21.4% (17.8%, 25.9%), respectively. Conclusions: This innovative approach utilizing our metabolic aging clock holds significant promise for accurately assessing biological age and enhancing our capacity to detect APL and CRC.

    View details for DOI 10.7150/thno.87303

    View details for PubMedID 38389840

    View details for PubMedCentralID PMC10879879

  • Exploring the feasibility of using long-term stored newborn dried blood spots to identify metabolic features for congenital heart disease screening. Biomarker research Ceresnak, S. R., Zhang, Y., Ling, X. B., Su, K. J., Tang, Q., Jin, B., Schilling, J., Chou, C. J., Han, Z., Floyd, B. J., Whitin, J. C., Hwa, K. Y., Sylvester, K. G., Chubb, H., Luo, R. Y., Tian, L., Cohen, H. J., McElhinney, D. B. 2023; 11 (1): 97


    Congenital heart disease (CHD) represents a significant contributor to both morbidity and mortality in neonates and children. There's currently no analogous dried blood spot (DBS) screening for CHD immediately after birth. This study was set to assess the feasibility of using DBS to identify reliable metabolite biomarkers with clinical relevance, with the aim to screen and classify CHD utilizing the DBS. We assembled a cohort of DBS datasets from the California Department of Public Health (CDPH) Biobank, encompassing both normal controls and three pre-defined CHD categories. A DBS-based quantitative metabolomics method was developed using liquid chromatography with tandem mass spectrometry (LC-MS/MS). We conducted a correlation analysis comparing the absolute quantitated metabolite concentration in DBS against the CDPH NBS records to verify the reliability of metabolic profiling. For hydrophilic and hydrophobic metabolites, we executed significant pathway and metabolite analyses respectively. Logistic and LightGBM models were established to aid in CHD discrimination and classification. Consistent and reliable quantification of metabolites were demonstrated in DBS samples stored for up to 15 years. We discerned dysregulated metabolic pathways in CHD patients, including deviations in lipid and energy metabolism, as well as oxidative stress pathways. Furthermore, we identified three metabolites and twelve metabolites as potential biomarkers for CHD assessment and subtypes classifying. This study is the first to confirm the feasibility of validating metabolite profiling results using long-term stored DBS samples. Our findings highlight the potential clinical applications of our DBS-based methods for CHD screening and subtype classification.

    View details for DOI 10.1186/s40364-023-00536-y

    View details for PubMedID 37957758

    View details for PubMedCentralID PMC10644604

  • Comparison of liquid chromatography-high-resolution tandem mass spectrometry (MS2) and multi-stage mass spectrometry (MS3) for screening toxic natural products. Journal of mass spectrometry and advances in the clinical lab Luo, R. Y., Comstock, K., Ding, C., Wu, A. H., Lynch, K. L. 2023; 30: 38-44


    Liquid chromatography-high-resolution mass spectrometry (LC-HR-MS) has emerged as a powerful analytical technology for compound screening in clinical toxicology. To evaluate the potential of LC-HR-MS3 in detecting toxic natural products, a spectral library of 85 natural products (79 alkaloids) that contains both MS2 and MS3 mass spectra was constructed and used to identify the natural products. Samples were analyzed using an LC-HR-MS3 method and the generated data were matched to the spectral library to identify the natural products.To test the performance of the LC-HR-MS3 method in different sample matrices, the 85 natural product standards were divided into three groups to separate structural isomers and avoid ion suppression effects caused by co-elution of multiple analytes. The grouped analytes were spiked into drug-free serum and drug-free urine to produce contrived clinical samples.The compound identification results of the 85 natural products in urine and serum samples were obtained. The match scores using both MS2 and MS3 mass spectra and those using only MS2 mass spectra were compared at 10 different analyte concentrations. The two types of data analysis provided identical identification results for the majority of the analytes (96% in serum, 92% in urine), whereas, for the remaining analytes, the MS2-MS3 tree data analysis had better performance in identifying them at lower concentrations.This study shows that in comparison to LC-HR-MS (MS2), LC-HR-MS3 can increase the performance in identification of a small group of the toxic natural products tested in serum and urine specimens.

    View details for DOI 10.1016/j.jmsacl.2023.09.002

    View details for PubMedID 37876549

    View details for PubMedCentralID PMC10590993

  • High-throughput quantitation of amino acids and acylcarnitine in cerebrospinal fluid: identification of PCNSL biomarkers and potential metabolic messengers. Frontiers in molecular biosciences Ma, J., Chen, K., Ding, Y., Li, X., Tang, Q., Jin, B., Luo, R. Y., Thyparambil, S., Han, Z., Chou, C. J., Zhou, A., Schilling, J., Lin, Z., Ma, Y., Li, Q., Zhang, M., Sylvester, K. G., Nagpal, S., McElhinney, D. B., Ling, X. B., Chen, B. 2023; 10: 1257079


    Background: Due to the poor prognosis and rising occurrence, there is a crucial need to improve the diagnosis of Primary Central Nervous System Lymphoma (PCNSL), which is a rare type of non-Hodgkin's lymphoma. This study utilized targeted metabolomics of cerebrospinal fluid (CSF) to identify biomarker panels for the improved diagnosis or differential diagnosis of primary central nervous system lymphoma (PCNSL). Methods: In this study, a cohort of 68 individuals, including patients with primary central nervous system lymphoma (PCNSL), non-malignant disease controls, and patients with other brain tumors, was recruited. Their cerebrospinal fluid samples were analyzed using the Ultra-high performance liquid chromatography - tandem mass spectrometer (UHPLC-MS/MS) technique for targeted metabolomics analysis. Multivariate statistical analysis and logistic regression modeling were employed to identify biomarkers for both diagnosis (Dx) and differential diagnosis (Diff) purposes. The Dx and Diff models were further validated using a separate cohort of 34 subjects through logistic regression modeling. Results: A targeted analysis of 45 metabolites was conducted using UHPLC-MS/MS on cerebrospinal fluid (CSF) samples from a cohort of 68 individuals, including PCNSL patients, non-malignant disease controls, and patients with other brain tumors. Five metabolic features were identified as biomarkers for PCNSL diagnosis, while nine metabolic features were found to be biomarkers for differential diagnosis. Logistic regression modeling was employed to validate the Dx and Diff models using an independent cohort of 34 subjects. The logistic model demonstrated excellent performance, with an AUC of 0.83 for PCNSL vs. non-malignant disease controls and 0.86 for PCNSL vs. other brain tumor patients. Conclusion: Our study has successfully developed two logistic regression models utilizing metabolic markers in cerebrospinal fluid (CSF) for the diagnosis and differential diagnosis of PCNSL. These models provide valuable insights and hold promise for the future development of a non-invasive and reliable diagnostic tool for PCNSL.

    View details for DOI 10.3389/fmolb.2023.1257079

    View details for PubMedID 38028545

    View details for PubMedCentralID PMC10644155

  • Development of a Urine Metabolomics Biomarker-Based Prediction Model for Preeclampsia during Early Pregnancy. Metabolites Zhang, Y., Sylvester, K. G., Jin, B., Wong, R. J., Schilling, J., Chou, C. J., Han, Z., Luo, R. Y., Tian, L., Ladella, S., Mo, L., Maric, I., Blumenfeld, Y. J., Darmstadt, G. L., Shaw, G. M., Stevenson, D. K., Whitin, J. C., Cohen, H. J., McElhinney, D. B., Ling, X. B. 2023; 13 (6)


    Preeclampsia (PE) is a condition that poses a significant risk of maternal mortality and multiple organ failure during pregnancy. Early prediction of PE can enable timely surveillance and interventions, such as low-dose aspirin administration. In this study, conducted at Stanford Health Care, we examined a cohort of 60 pregnant women and collected 478 urine samples between gestational weeks 8 and 20 for comprehensive metabolomic profiling. By employing liquid chromatography mass spectrometry (LCMS/MS), we identified the structures of seven out of 26 metabolomics biomarkers detected. Utilizing the XGBoost algorithm, we developed a predictive model based on these seven metabolomics biomarkers to identify individuals at risk of developing PE. The performance of the model was evaluated using 10-fold cross-validation, yielding an area under the receiver operating characteristic curve of 0.856. Our findings suggest that measuring urinary metabolomics biomarkers offers a noninvasive approach to assess the risk of PE prior to its onset.

    View details for DOI 10.3390/metabo13060715

    View details for PubMedID 37367874

  • Mass spectrometry quantitation of immunosuppressive drugs in clinical specimens using online solid-phase extraction and accurate-mass full scan-single ion monitoring. Journal of mass spectrometry and advances in the clinical lab Yeung, P. S., Miller, P., Lai-Nyugen, T. B., Cheng, P., Ibrahim, A., Shi, R., Bowen, R. A., Luo, R. Y. 2023; 28: 99-104


    Introduction: Therapeutic drug monitoring (TDM) of immunosuppressants is essential for optimal care of transplant patients. Immunoassays and liquid chromatography-mass spectrometry (LC-MS) are the most commonly used methods for TDM. However, immunoassays can suffer from interference from heterophile antibodies and structurally similar drugs and metabolites. Additionally, nominal-mass LC-MS assays can be difficult to optimize and are limited in the number of detectable compounds.Objectives: The aim of this study was to implement a mass spectrometry-based test for immunosuppressant TDM using online solid-phase extraction (SPE) and accurate-mass full scan-single ion monitoring (FS-SIM) data acquisition mode.Methods: LC-MS analysis was performed on a TLX-2 multi-channel HPLC with a Q-Exactive Plus mass spectrometer. TurboFlow online SPE was used for sample clean up. The accurate-mass MS was set to positive electrospray ionization mode with FS-SIM for quantitation of tacrolimus, sirolimus, everolimus, and cyclosporine A. MS2 fragmentation pattern was used for compound confirmation.Results: The method was validated in terms of precision, analytical bias, limit of quantitation, linearity, carryover, sample stability, and interference. Quantitation of tacrolimus, sirolimus, everolimus, and cyclosporine A correlated well with results from an independent reference laboratory (r=0.926-0.984).Conclusions: Accurate-mass FS-SIM can be successfully utilized for immunosuppressant TDM with good correlation with results generated by standard methods. TurboFlow online SPE allows for a simple "protein crash and shoot" sample preparation protocol. Compared to traditional MRM, analyte quantitation by FS-SIM facilitates a streamlined assay optimization process.

    View details for DOI 10.1016/j.jmsacl.2023.03.002

    View details for PubMedID 36937810

  • Accurate Identification of Hemoglobin Variants By Top-Down Protein Analysis Using Capillary Electrophoresis-HighResolution Mass Spectrometry Luo, R., Wong, C., Xia, J., Glader, B., Shi, R., Zehnder, J. L. AMER SOC HEMATOLOGY. 2022: 5384-5386
  • Serum peptidomic screening identified circulating peptide biomarkers predictive for preeclampsia. Frontiers in cardiovascular medicine Zhao, S., Yin, C., Zhai, Y., Jia, Z., Su, S., Lu, Y., Meng, L., Li, C., Liu, X., Cong, Y., Li, Y., Liu, Y., Chen, L., Wang, J., Xu, Z., Zheng, Y., Sun, Z., Luo, R. Y., Yu, X., Yang, H. S., Liu, X., Zhao, Z., Cao, Z. 2022; 9: 946433


    Background: Reliable biomarkers are needed to improve preeclampsia (PE) prediction accuracy. With the investigational tool of peptidomics, we aimed to identify and validate potential serum peptide biomarkers in cohorts suspected for PE development in middle or late pregnancy.Methods: Totally 195 serum samples were prospectively collected from pregnant women with PE-related syndromes who were followed up for PE development until delivery. Serum peptidomic analysis was performed in the discovery cohort of 115 samples using matrix-assisted laser desorption ionization-time of flight coupled with Linear Trap Quadropole Orbitrap mass spectrometry. The candidate biomarkers were further validated using an in-house developed liquid chromatography tandem mass spectrometry (LC-MS/MS) method in an independent validation cohort of 80 serum samples.Results: We identified 8 peptides that were differentially expressed and originated from fibrinogen alpha chain (FGA), inter-alpha-trypsin inhibitor heavy chain H4 (ITIH4) and complement component 3. In the subsequent LC-MS/MS quantitation analysis, the levels of the three peptides (FGA-1033.4, ITIH4-2026.9, ITIH4-2051.1) exhibited a significant difference between the PE-positive and PE-negative groups. Further, the three-peptide panel yielded an area under the ROC curve (AUC) of 0.985 [95% confidence interval (CI) 0.965-1.000] and 0.923 (95% CI 0.845-1.000) in the discovery and validation cohorts respectively, with negative predictive values of 98.1-98.8% and positive predictive values of 73.1-85.3% that were much improved when compared with that of soluble fms-like tyrosine kinase-1/placental growth factor (sFlt-1/PlGF) ratio.Conclusions: We have discovered and validated a novel three-peptide biomarker panel predictive for the occurrence PE in pregnant women.

    View details for DOI 10.3389/fcvm.2022.946433

    View details for PubMedID 36304541

  • Primary Hyperparathyroidism in Pregnancy: Insights From a Case of a 28-Year-Old Woman With Miscarriages and Hyperemesis Gravidarum ANNALS OF LABORATORY MEDICINE Zhang, L., Luo, Y., Hu, Y., Zhai, Y., Gao, H., Cao, Z. 2021; 41 (3): 336-338

    View details for DOI 10.3343/alm.2021.41.3.336

    View details for Web of Science ID 000598521800012

    View details for PubMedID 33303721

    View details for PubMedCentralID PMC7748091

  • Establishment of a High-Resolution Liquid Chromatography-Mass Spectrometry Spectral Library for Screening Toxic Natural Products. Journal of analytical toxicology Luo, Y. R., Goodnough, R., Yun, C., Wu, A. H., Lynch, K. L. 2021


    Many natural products have biological effects on humans and animals. Poisoning caused by natural products is common in clinical toxicology cases. Liquid chromatography-high-resolution-mass spectrometry (LC-HRMS) has recently emerged as a powerful analytical tool for large-scale target screening, and the application of LC-HRMS can be expanded to evaluate potential natural product poisoning in clinical cases. We report the construction of an LC-HRMS spectral library of 95 natural products commonly implicated in poisoning, and an LC-HRMS assay was validated for definitive detection of natural products in urine and serum samples. For each compound, the limit of detection (LOD) was determined in the analytical range of 1.0 - 1000 ng/mL for urine samples and 0.50 - 500 ng/mL for serum samples. The mean (SD) of matrix effects for urine samples and that for serum samples were both -21% (22%), and the mean (SD) of recovery for serum samples was 89% (26%). The LC-HRMS assay was successfully applied to identify natural products in clinical cases. The spectral library parameters of each compound are provided in the supplementary material to aid other laboratories in identification of unknown natural toxins and development of similar methods on different mass spectrometry platforms.

    View details for DOI 10.1093/jat/bkab015

    View details for PubMedID 33506876

  • Simultaneous quantitation of four androgens and 17-hydroxyprogesterone in polycystic ovarian syndrome patients by LC-MS/MS JOURNAL OF CLINICAL LABORATORY ANALYSIS Cao, Z., Lu, Y., Cong, Y., Liu, Y., Li, Y., Wang, H., Zhang, Q., Huang, W., Liu, J., Dong, Y., Tang, G., Luo, Y. R., Yin, C., Zhai, Y. 2020; 34 (12): e23539


    Due to the low concentration of androgens in women and the limitation of immunoassays, it remains a challenge to accurately determine the levels of serum androgens in polycystic ovary syndrome (PCOS) patients for clinical laboratories. In this report, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous quantitation of testosterone (T), androstenedione (A4), dehydroepiandrosterone sulfate (DHEAS), dihydrotestosterone (DHT), and 17-hydroxyprogesterone (17-OHP) that are associated with PCOS.The serum samples were processed by protein precipitation and solid phase extraction before analysis with the in-house developed LC-MS/MS. The chromatographic separation was achieved with a C18 column, using a linear gradient elution with two mobile phases: 0.02% formic acid in water (phase A) and 0.1% formic acid in methanol (phase B). The separated analytes were detected by positive or negative electrospray ionization mode under multiple reaction monitoring (MRM).The assay for all the five analytes was linear, stable, with imprecision less than 9% and recoveries within ±10%. The lower limits of quantification were 0.05, 0.05, 5, 0.025, and 0.025 ng/mL for T, A4, DHEAS, DHT, and 17-OHP, respectively. In the receiver operating characteristic curve (ROC) analyses with the PCOS (n = 63) and healthy (n = 161) subjects, the AUC of the four-androgen combined was greater than that of any single androgen tested in PCOS diagnosis.The LC-MS/MS method for the four androgens and 17-OHP showed good performance for clinical implementation. More importantly, simultaneous quantitation of the four androgens provided better diagnostic power for PCOS.

    View details for DOI 10.1002/jcla.23539

    View details for Web of Science ID 000561078200001

    View details for PubMedID 32820576

    View details for PubMedCentralID PMC7755789

  • A case of unexplained duodenal ulcer and massive gastrointestinal bleed CLINICA CHIMICA ACTA Luo, Y., Goodnough, R., Menza, R., Badea, A., Luu, H., Kornblith, L. Z., Lynch, K. L. 2020; 506: 188-190


    A 73-year-old man was displaying symptoms of massive gastrointestinal (GI) bleed. Surgical actions were performed to control the bleed caused by an erosive duodenal ulcer with duodenal perforation. When investigating the culprit of this case, the pain medications prescribed two weeks prior by a traditional Chinese medicine doctor raised attention. The patient's admission serum sample and the pain medications from unknown sources were analyzed using a clinically validated liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method. The NSAIDs diclofenac, piroxicam, and indomethacin were identified, as well as some other synthetic drugs and natural products. The patient's concurrent exposure to multiple NSAIDs significantly increased the risk of upper GI complications. It is reasonable to argue that the high-dose use of the NSAIDs was a major cause of the duodenal ulcer and GI bleed. In addition, the identified natural products such as atropine and ephedrine have well-documented toxicities. It is important to increase the visibility of unregulated medications, and the capability to perform untargeted mass spectrometry analysis provides a unique diagnostic advantage in cases where exposure to toxic substances is possible.

    View details for DOI 10.1016/j.cca.2020.03.037

    View details for Web of Science ID 000534370700029

    View details for PubMedID 32234495

  • A thin-film interferometry-based label-free immunoassay for the detection of daratumumab interference in serum protein electrophoresis CLINICA CHIMICA ACTA Luo, Y., Chakraborty, I., Zuk, R. F., Lynch, K. L., Wu, A. B. 2020; 502: 128-132


    Daratumumab (DARA) is a fully human anti-CD38 IgG1-κ monoclonal antibody drug used in the treatment of multiple myeloma (MM). While serum protein electrophoresis (SPEP) is an important assay for diagnosis and monitoring of patients with MM, DARA can appear in the γ-region as a single band and interfere with the interpretation of SPEP results. An approach to detect the interference is measuring the quantity of DARA in serum samples and assessing its impact on SPEP results. Immunoassays based on label-free technologies, i.e. label-free immunoassays (LFIA's), can achieve real-time immunometric measurement without attaching a reporter molecule (enzyme, fluorophore, etc.) to the immunocomplex. The recorded time course of the immunocomplex formation allows for quantitation on initial binding rate, which facilitates rapid measurement within a few minutes. Based on the thin-film interferometry (TFI) technology, a rapid LFIA was established for the quantitation of DARA in serum samples.The TFI-based LFIA for DARA was validated for imprecision (CV), accuracy, limit of quantitation (LOQ), and analytical measurement range (AMR). Interference to the LFIA was evaluated using a group of protein samples, as well as hemolytic, lipemic, and icteric clinical samples.The precision of the TFI-based LFIA's for DARA ranged from 6.5% to 10.7% (within-run CV), and 7.4% to 11.6% (between-run CV), with a bias of -2.1% to 10.1%. The LOQ was 10 μg/ml (n = 4, CV 9.8%), with an AMR ranging from the LOQ to 1000 μg/ml. The LFIA was used to measure 37 patient samples submitted for SPEP testing. The LFIA results were 100% consistent with the history of DARA use as documented in the medical record.The TFI-based LFIA was successful at accurately identifying DARA in serum samples and can be used to identify DARA interference in SPEP testing. This work demonstrates the applicability of label-free technologies, particularly the TFI technology, to clinical diagnostic needs. Given the simplicity and the speed of the testing process, the TFI technology provides a unique testing approach for the measurement of proteins in clinical samples.

    View details for DOI 10.1016/j.cca.2019.12.019

    View details for Web of Science ID 000512220200017

    View details for PubMedID 31883925

  • Label-Free Detection of Therapeutic Monoclonal Antibody Interference Luo, Y. R. American Association for Clinical Chemistry. 2020 ; Clinical Laboratory News
  • Is High-Resolution Liquid Chromatography-Multistage Mass Spectrometry (LC-HR-MSn) a Good Choice for Screening Toxic Natural Products? Luo, Y. R. American Association for Clinical Chemistry. 2020 ; AACC Academy’s Scientific Shorts
  • Correlation of Breath and Blood Delta(9)-Tetrahydrocannabinol Concentrations and Release Kinetics Following Controlled Administration of Smoked Cannabis CLINICAL CHEMISTRY Lynch, K. L., Luo, Y., Hooshfar, S., Yun, C. 2019; 65 (9): 1171-1179


    Cannabis use results in impaired driving and an increased risk of motor vehicle crashes. Cannabinoid concentrations in blood and other matrices can remain high long after use, prohibiting the differentiation between acute and chronic exposure. Exhaled breath has been proposed as an alternative matrix in which concentrations may more closely correspond to the window of impairment; however, efficient capture and analytically sensitive detection methods are required for measurement.Timed blood and breath samples were collected from 20 volunteers before and after controlled administration of smoked cannabis. Cannabinoid concentrations were measured using LC-MS/MS to determine release kinetics and correlation between the 2 matrices.Δ9-Tetrahydrocannabinol (THC) was detected in exhaled breath for all individuals at baseline through 3 h after cannabis use. THC concentrations in breath were highest at the 15-min timepoint (median = 17.8 pg/L) and declined to <5% of this concentration in all participants 3 h after smoking. The decay curve kinetics observed for blood and breath were highly correlated within individuals and across the population.THC can be reliably detected throughout the presumed 3-h impairment window following controlled administration of smoked cannabis. The findings support breath THC concentrations as representing a physiological process and are correlated to blood concentrations, albeit with a shorter window of detection.

    View details for DOI 10.1373/clinchem.2019.304501

    View details for Web of Science ID 000484370100016

    View details for PubMedID 31296552

  • Azo coupling-based derivatization method for high-sensitivity liquid chromatography-tandem mass spectrometry analysis of tetrahydrocannabinol and other aromatic compounds JOURNAL OF CHROMATOGRAPHY A Luo, Y., Han, J., Yun, C., Lynch, K. L. 2019; 1597: 109-118


    An azo coupling-based derivatization method is reported for high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS) quantitation of tetrahydrocannabinol (THC) and other aromatic compounds, i.e. phenols and amines. Through the azo coupling of a diazonium to an analyte, it produces a derivatized analyte which has enhanced ionization efficiency and results in high-response fragments in tandem mass spectrometry. The derivatization method was applied to six typical aromatic compounds using three different diazonium salts as derivatization reagents, demonstrating its applicability to a variety of analytes and reagents. The derivatization reaction can be directly carried out in neat samples, and after derivatization the samples can be immediately sent to the LC-MS/MS instrument for analysis. These advantages facilitate a one-step sample preparation procedure that can be completed in less than one hour, allowing for a "derivatize & shoot" lab workflow. The derivatization method was applied to establish an LC-MS/MS assay for the quantitation of THC in human breath samples. The derivatization conditions were studied in this application, including the effects of acidity, organic solvent, and diazonium concentration in the reaction. The THC derivatization assay was validated and achieved a limit of quantitation (LOQ) of 0.50 pg/ml using either of the two regio-isomers of the azo-derivative of THC (THC-DRV). To prove that the derivatization method has compatibility with complex-matrix samples, a THC derivatization assay for serum samples was established, in which the azo coupling reaction was directly carried out in crude protein-precipitated supernatants. An LOQ of 5.0 pg/ml was achieved. In addition, excellent correlation between THC derivatization and non-derivatization assays was found in the analysis of whole blood samples.

    View details for DOI 10.1016/j.chroma.2019.03.022

    View details for Web of Science ID 000469896000012

    View details for PubMedID 30910385

  • Quantitation of Cannabinoids in Breath Samples Using a Novel Derivatization LC-MS/MS Assay with Ultra-High Sensitivity JOURNAL OF ANALYTICAL TOXICOLOGY Luo, Y., Yun, C., Lynch, K. L. 2019; 43 (5): 331-339


    As the legalization of medical and recreational marijuana use expands, measurement of tetrahydrocannabinol (THC) in human breath has become an area of interest. The presence and concentration of cannabinoids in breath have been shown to correlate with recent marijuana use and may be correlated with impairment. Given the low concentration of THC in human breath, sensitive analytical methods are required to further evaluate its utility and window of detection. This paper describes a novel derivatization method based on an azo coupling reaction that significantly increases the ionization efficiency of cannabinoids for LC-MS/MS analysis. This derivatization reaction allows for a direct derivatization reaction with neat samples and does not require further sample clean-up after derivatization, thus facilitating an easy and rapid "derivatize & shoot" sample preparation. The derivatization assay allowed for limits of quantitation (LOQ's) in the sub-pg/mL to pg/mL range for the five cannabinoids in breath samples, i.e., only 5~50 femtograms of an analyte was required for quantitation in a single analysis. This ultrahigh sensitivity allowed for the quantitation of cannabinoids in all breath samples collected within 3 hours of smoking cannabis (n = 180). A linear correlation between THC and cannabinol (CBN) in human breath was observed, supporting the hypothesis that CBN is converted from THC during the combustion of cannabis. The derivatization method was also applied to the analysis of cannabinoids in whole blood samples, achieving LOQ's at ten-pg/mL to sub-ng/mL level. This azo coupling-based derivatization approach provided the needed analytical sensitivity for the analysis of THC in human breath samples using LC-MS/MS and could be a valuable tool for the analysis of other aromatic compounds in the future.

    View details for DOI 10.1093/jat/bkz023

    View details for Web of Science ID 000482413200003

    View details for PubMedID 30951168

  • Drug Induced Liver Injury and Lactic Acidosis Associated with Chronic Sustained Release Nicotinamide Exposure American Journal of Biomedical Science & Research Goodnough, R., Monto, A., Luo, Y. R., Lynch, K. L., Blanc, P. D. 2019; 5 (2): 000894
  • Ligand Immobilization in Protein Interaction Studies – An Unattended Amine Coupling Protocol with Automatic Coinjection Activation Luo, R., Bronner, V., Zafir-Lavie, I., Thornton, K., Shezifi, D. Bio-Rad Laboratories. 2014 ; Bioradiations
  • Novel Liposome-Capture Surface Chemistries to Analyze Drug-Lipid Interaction Using the ProteOn™ XPR36 System Edri, M., Luo, R., Rabkin, E., Nimri, S., Shezifi, D. Bio-Rad Laboratories. 2014 ; Bioradiations
  • Analyzing Binding Kinetics with Surface Plasmon Resonance Complemented with Direct Mass Spectrometry on the Same Sensor Chip Luo, R., Zhu, M., Roth, S., Plows, F. Bio-Rad Laboratories. 2013 ; Bioradiations
  • A Novel Biotinylated Ligand-Capture Method with Surface Regeneration Capability for Label-Free Biomolecular Interaction Analysis Zhu, M., Shezifi, D., Nimri, S., Luo, R. Bio-Rad Laboratories. 2013 ; Bioradiations
  • Immobilization of Active Kinases for Small Molecule Inhibition Studies Popplewell, J., Luo, R. Bio-Rad Laboratories. 2013 ; Bioradiations
  • Microfluidic Device for Coupling Capillary Electrophoresis and Matrix-Assisted Laser Desorption Ionization-Mass Spectrometry JALA Luo, Y., Xu, S., Schilling, J. W., Lau, K. H., Whitin, J. C., Yu, T. T., Cohen, H. J. 2009; 14 (5): 252-261
  • Perforated membrane method for fabricating three-dimensional polydimethylsiloxane microfluidic devices LAB ON A CHIP Luo, Y., Zare, R. N. 2008; 8 (10): 1688-1694


    A procedure is described for making layer-to-layer interconnections in polydimethylsiloxane (PDMS) microfluidic devices. Thin (approximately 50 microm) perforated PDMS membranes are bonded to thicker (0.1 cm or more) PDMS slabs by means of thermally cured PDMS prepolymer to form a three-dimensional (3D) channel structure, which may contain channel or valve arrays that can pass over and under one another. Devices containing as many as two slabs and three perforated membranes are demonstrated. We also present 3D PDMS microfluidic devices for display and for liquid dispensing.

    View details for DOI 10.1039/b807751g

    View details for Web of Science ID 000260466300013

    View details for PubMedID 18813392

  • Microfluidic device for immunoassays based on surface plasmon resonance imaging LAB ON A CHIP Luo, Y., Yu, F., Zare, R. N. 2008; 8 (5): 694-700


    We have designed and fabricated a polydimethylsiloxane (PDMS) microfluidic device containing an array of gold spots onto which antigens or antibodies of interest can be attached. We use surface plasmon resonance (SPR) imaging to monitor the antibody-antigen recognition and binding events. This combination offers two significant advantages: (1) the microfluidic device dramatically reduces reaction time and sample consumption; and (2) the SPR imaging yields real-time detection of the immunocomplex formation. Thus, an immunoreaction may be detected and quantitatively characterized in about 10 min. The sensitivity of this method is at the subnanomolar level. When gold nanoparticles are selectively coupled to the immunocomplex to cause signal amplification, the sensitivity reaches the ten to one hundred picomolar level but the time required increases to about 60 min.

    View details for DOI 10.1039/b800606g

    View details for Web of Science ID 000255276700009

    View details for PubMedID 18432338

  • Controlling electroosmotic flow in poly(dimethylsiloxane) separation channels by means of prepolymer additives ANALYTICAL CHEMISTRY Luo, Y., Huang, B., Wu, H., Zare, R. N. 2006; 78 (13): 4588-4592


    The electroosmotic flow (EOF) in a poly(dimethylsiloxane) (PDMS) separation channel can be altered and controlled by adding a carboxylic acid to the prepolymer prior to curing. When the prepolymer is doped with 0.5 wt % undecylenic acid (UDA), the electroosmotic mobility in a modified PDMS channel rises to (7.6 +/- 0.2) x 10(-4) cm(2) V(-1) s(-1) (in HEPES buffer at pH 8.5), which is nearly twice that in the native PDMS channel. Because this modification does not significantly change the hydrophobicity of the PDMS surface, it is possible to combine the modified PDMS with a dynamic coating of n-dodecyl beta-d-maltoside (DDM), which prevents protein sticking (see Huang, B.; Wu, H. K.; Kim, S.; Zare, R. N. Lab Chip 2005, 5, 1005-1007). The modified PDMS channel with a dynamic coating of DDM generates an electroosmotic mobility of (5.01 +/- 0.09) x 10(-4) cm(2) V(-1) s(-1), which shows excellent reproducibility both in successive runs and during storage in water. Combining this surface modification and the dynamic coating of DDM is an effective means for both providing stable EOF in the PDMS channels and preventing protein adsorption on the channel walls. To demonstrate these effects, we show that the electrophoretic separation of immunocomplexes in free solution can be readily accomplished in a microfluidic chip made of UDA-doped (0.5 wt %) PDMS with a dynamic coating of DDM.

    View details for DOI 10.1021/ac052274g

    View details for Web of Science ID 000238665200047

    View details for PubMedID 16808469

  • Optimized separation of isoquinoline alkaloids in Thalictrum herbal medicine by microemulsion electrokinetic chromatography JOURNAL OF LIQUID CHROMATOGRAPHY & RELATED TECHNOLOGIES Luo, Y. Q., Bo, T., Li, M., Gong, S. X., Li, K. A., Liu, H. W. 2003; 26 (11): 1719-1730
  • Separation of isoquinoline alkaloids and saponins by microemulsion electrokinetic chromatography with anionic and cationic surfactants CHROMATOGRAPHIA Bo, T., Zhong, L., Li, M., Luo, Y. Q., Li, K. A., Liu, H. W., Guo, D. A. 2002; 56 (11-12): 709-716

    View details for DOI 10.1007/BF02492472

    View details for Web of Science ID 000179861600008