Ruben Y. Luo

All Publications

• 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

  Abstract

  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

  Abstract

  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

  Abstract

  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

  Abstract

  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

• 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

  Abstract

  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

• 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

  View details for DOI 10.1182/blood-2022-170457

  View details for Web of Science ID 000893223205184

• 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

  Abstract

  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

  Abstract

  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

  Abstract

  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

  Abstract

  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

  Abstract

  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

  Abstract

  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

• 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

  Abstract

  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

  View details for DOI 10.34297/ajbsr.2019.05.000894

• 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
• 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
• 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
• 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

  View details for DOI 10.1016/j.jala.2009.02.005

  View details for Web of Science ID 000285163200003

• Perforated membrane method for fabricating three-dimensional polydimethylsiloxane microfluidic devices LAB ON A CHIP Luo, Y., Zare, R. N. 2008; 8 (10): 1688-1694

  Abstract

  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

  Abstract

  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

  Abstract

  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

  View details for DOI 10.1081/JLC-120021279

  View details for Web of Science ID 000184005600004

• 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