Zhen is from China and gained his Bachelor of Science at Beihang University. He pursued his next-level education in the US as he went to Brown University in 2017. At Brown, he did his PhD with Prof. Vicki Colvin to work on magnetic nanomaterials and their biomedical applications. He developed a systematic synthesis for the iron oxide nanocrystal clusters and reported the superior magnetic properties to conventional single-core nanoparticles. Working with multidisciplinary collaborators, Zhen has achieved many in vitro and in vivo studies applying these materials and demonstrated excellent cell separation efficiency, drug delivery, hyperthermia cancer treatment, and contrast agent for imaging using the clusters. Now at Stanford, Zhen joined Dr. Jianghong Rao's lab and is working on the detection and imaging of pathogens and cancers with nanomaterials, especially using magnetic particle imaging (MPI). It is Zhen’s desire to push magnetic nanotechnologies for broader applications in biomedicines.

Honors & Awards

  • ACS Division of Colloid and Surface Chemistry Outstanding Student Poster Award, American Chemical Society (2022)
  • Philip A. Smith ’26 Chemistry Fellowship, Brown University (2018)
  • Shenyuan Medal, the Highest Undergraduate Honor, Beihang University (2017)
  • Nano Research Paper of the Month Award, Tsinghua University Press (2016)

Boards, Advisory Committees, Professional Organizations

  • Guest Editor, Special Issue "Semiconductor Nanomaterials for Energy Conversion and Environmental Applications" in Crystal, MDPI (2022 - 2022)

Stanford Advisors

Current Research and Scholarly Interests

Applying magnetic nanomaterials for bioimaging and cancer treatment

Lab Affiliations

All Publications

  • Culture-Independent Multiplexed Detection of Drug-Resistant Bacteria Using Surface-Enhanced Raman Scattering. ACS sensors Dai, T., Xiao, Z., Shan, D., Moreno, A., Li, H., Prakash, M., Banaei, N., Rao, J. 2023


    The rapid and accurate detection of bacteria resistance to β-lactam antibiotics is critical to inform optimal treatment and prevent overprescription of potent antibiotics. Here, we present a fast, culture-independent method for the detection of extended-spectrum β-lactamases (ESBLs) using surface-enhanced Raman scattering (SERS). The method uses Raman probes that release sulfur-based Raman active molecules in the presence of β-lactamases. The released thiol molecules can be captured by gold nanoparticles, leading to amplified Raman signals. A broad-spectrum cephalosporin probe R1G and an ESBL-specific probe R3G are designed to enable duplex detection of bacteria expressing broad-spectrum β-lactamases or ESBLs with a detection limit of 103 cfu/mL in 1 h incubation. Combined with a portable Raman microscope, our culturing-free SERS assay has reduced screening time to 1.5 h without compromising sensitivity and specificity.

    View details for DOI 10.1021/acssensors.3c01345

    View details for PubMedID 37506677

  • Sensitive T2 MRI Contrast Agents from the Rational Design of Iron Oxide Nanoparticle Surface Coatings JOURNAL OF PHYSICAL CHEMISTRY C Cho, M., Villanova, J., Ines, D. M., Chen, J., Lee, S., Xiao, Z., Guo, X., Dunn, J. A., Stueber, D. D., Decuzzi, P., Colvin, V. L. 2023; 127 (2): 1057-1070
  • Multifunctional Magnetic Nanoclusters Can Induce Immunogenic Cell Death and Suppress Tumor Recurrence and Metastasis. ACS nano Zhang, L., Zhang, Q., Hinojosa, D. T., Jiang, K., Pham, Q. K., Xiao, Z., Colvin, V. L., Bao, G. 2022


    Metastasis is the predominant cause of cancer deaths due to solid organ malignancies; however, anticancer drugs are not effective in treating metastatic cancer. Here we report a nanotherapeutic approach that combines magnetic nanocluster-based hyperthermia and free radical generation with an immune checkpoint blockade (ICB) for effective suppression of both primary and secondary tumors. We attached 2,2'-azobis(2-midinopropane) dihydrochloride (AAPH) molecules to magnetic iron oxide nanoclusters (IONCs) to form an IONC-AAPH nanoplatform. The IONC can generate a high level of localized heat under an alternating magnetic field (AMF), which decomposes the AAPH on the cluster surface and produces a large number of carbon-centered free radicals. A combination of localized heating and free radicals can effectively kill tumor cells under both normoxic and hypoxic conditions. The tumor cell death caused by the combination of magnetic heating and free radicals led to the release or exposure of various damage-associated molecule patterns, which promoted the maturation of dendritic cells. Treating the tumor-bearing mice with IONC-AAPH under AMF not only eradicated the tumors but also generated systemic antitumor immune responses. The combination of IONC-AAPH under AMF with anti-PD-1 ICB dramatically suppressed the growth of untreated distant tumors and induced long-term immune memory. This IONC-AAPH based magneto-immunotherapy has the potential to effectively combat metastasis and control cancer recurrence.

    View details for DOI 10.1021/acsnano.2c06776

    View details for PubMedID 36306738

  • Increasing the antioxidant capacity of ceria nanoparticles with catechol-grafted poly(ethylene glycol). Journal of materials chemistry. B Hu, Y., Zhang, Q., Garcia-Rojas, D., Ling, V., Masterson, C. M., Bi, Y., Xiao, Z., Guo, X., Villanova, J., Dunn, J., Colvin, V. L. 2022


    Ceria nanoparticles are remarkable antioxidants due to their large cerium(III) content and the possibility of recovering cerium(III) from cerium(IV) after reaction. Here we increase the cerium(III) content of colloidally stable nanoparticles (e.g., nanocrystals) using a reactive polymeric surface coating. Catechol-grafted poly(ethylene glycols) (PEG) polymers of varying lengths and architectures yield materials that are non-aggregating in a variety of aqueous media. Cerium(IV) on the ceria surface both binds and oxidizes the catechol functionality, generating a dark-red colour emblematic of surface-oxidized catechols with a concomitant increase in cerium(III) revealed by X-ray photoemission spectroscopy (XPS). The extent of ceria reduction depends sensitively on the architecture of the coating polymer; small and compact polymer chains pack with high density at the nanoparticle surface yielding the most cerium(III). Nanoparticles with increased surface reduction, quantified by the intensity of their optical absorption and thermogravimetric measures of polymer grafting densities, were more potent antioxidants as measured by a standard TEAC antioxidant assay. For the same core composition nanoparticle antioxidant capacities could be increased over an order of magnitude by tailoring the length and architecture of the reactive surface coatings.

    View details for DOI 10.1039/d2tb00779g

    View details for PubMedID 36156670

  • When function is biological: Discerning how silver nanoparticle structure dictates antimicrobial activity. iScience Zhang, Q., Hu, Y., Masterson, C. M., Jang, W., Xiao, Z., Bohloul, A., Garcia-Rojas, D., Puppala, H. L., Bennett, G., Colvin, V. L. 2022; 25 (7): 104475


    Silver nanomaterials have potent antibacterial properties that are the foundation for their wide commercial use as well as for concerns about their unintended environmental impact. The nanoparticles themselves are relatively biologically inert but they can undergo oxidative dissolution yielding toxic silver ions. A quantitative relationship between silver material structure and dissolution, and thus antimicrobial activity, has yet to be established. Here, this dissolution process and associated biological activity is characterized using uniform nanoparticles with variable dimension, shape, and surface chemistry. From this, a phenomenological model emerges that quantitatively relates material structure to both silver dissolution and microbial toxicity. Shape has the most profound influence on antibacterial activity, and surprisingly, surface coatings the least. These results illustrate how material structure may be optimized for antimicrobial properties and suggest strategies for minimizing silver nanoparticle effects on microbes.

    View details for DOI 10.1016/j.isci.2022.104475

    View details for PubMedID 35789852

  • Subsecond multichannel magnetic control of select neural circuits in freely moving flies. Nature materials Sebesta, C., Torres Hinojosa, D., Wang, B., Asfouri, J., Li, Z., Duret, G., Jiang, K., Xiao, Z., Zhang, L., Zhang, Q., Colvin, V. L., Goetz, S. M., Peterchev, A. V., Dierick, H. A., Bao, G., Robinson, J. T. 2022


    Precisely timed activation of genetically targeted cells is a powerful tool for the study of neural circuits and control of cell-based therapies. Magnetic control of cell activity, or 'magnetogenetics', using magnetic nanoparticle heating of temperature-sensitive ion channels enables remote, non-invasive activation of neurons for deep-tissue applications and freely behaving animal studies. However, the in vivo response time of thermal magnetogenetics is currently tens of seconds, which prevents precise temporal modulation of neural activity. Moreover, magnetogenetics has yet to achieve in vivo multiplexed stimulation of different groups of neurons. Here we produce subsecond behavioural responses in Drosophila melanogaster by combining magnetic nanoparticles with a rate-sensitive thermoreceptor (TRPA1-A). Furthermore, by tuning magnetic nanoparticles to respond to different magnetic field strengths and frequencies, we achieve subsecond, multichannel stimulation. These results bring magnetogenetics closer to the temporal resolution and multiplexed stimulation possible with optogenetics while maintaining the minimal invasiveness and deep-tissue stimulation possible only by magnetic control.

    View details for DOI 10.1038/s41563-022-01281-7

    View details for PubMedID 35761060

  • Synthesis and Application of Magnetic Nanocrystal Clusters INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH Xiao, Z., Zhang, L., Colvin, V. L., Zhang, Q., Bao, G. 2022; 61 (22): 7613-7625
  • Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition JOVE-JOURNAL OF VISUALIZED EXPERIMENTS Effman, S., Avidan, S., Xiao, Z., Colvin, V. 2022


    Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

    View details for DOI 10.3791/63140

    View details for Web of Science ID 000802505600046

    View details for PubMedID 35188111

  • Controlled oxidation and surface modification increase heating capacity of magnetic iron oxide nanoparticles APPLIED PHYSICS REVIEWS Jiang, K., Zhang, Q., Hinojosa, D., Zhang, L., Xiao, Z., Yin, Y., Tong, S., Colvin, V. L., Bao, G. 2021; 8 (3)

    View details for DOI 10.1063/5.0042478

    View details for Web of Science ID 000675179900001

  • Magnetic Nanoparticles in Biology and Medicine: Past, Present, and Future Trends PHARMACEUTICS Stueber, D. D., Villanova, J., Aponte, I., Xiao, Z., Colvin, V. L. 2021; 13 (7)


    The use of magnetism in medicine has changed dramatically since its first application by the ancient Greeks in 624 BC. Now, by leveraging magnetic nanoparticles, investigators have developed a range of modern applications that use external magnetic fields to manipulate biological systems. Drug delivery systems that incorporate these particles can target therapeutics to specific tissues without the need for biological or chemical cues. Once precisely located within an organism, magnetic nanoparticles can be heated by oscillating magnetic fields, which results in localized inductive heating that can be used for thermal ablation or more subtle cellular manipulation. Biological imaging can also be improved using magnetic nanoparticles as contrast agents; several types of iron oxide nanoparticles are US Food and Drug Administration (FDA)-approved for use in magnetic resonance imaging (MRI) as contrast agents that can improve image resolution and information content. New imaging modalities, such as magnetic particle imaging (MPI), directly detect magnetic nanoparticles within organisms, allowing for background-free imaging of magnetic particle transport and collection. "Lab-on-a-chip" technology benefits from the increased control that magnetic nanoparticles provide over separation, leading to improved cellular separation. Magnetic separation is also becoming important in next-generation immunoassays, in which particles are used to both increase sensitivity and enable multiple analyte detection. More recently, the ability to manipulate material motion with external fields has been applied in magnetically actuated soft robotics that are designed for biomedical interventions. In this review article, the origins of these various areas are introduced, followed by a discussion of current clinical applications, as well as emerging trends in the study and application of these materials.

    View details for DOI 10.3390/pharmaceutics13070943

    View details for Web of Science ID 000677383400001

    View details for PubMedID 34202604

    View details for PubMedCentralID PMC8309177

  • 2D Gadolinium Oxide Nanoplates as T-1 Magnetic Resonance Imaging Contrast Agents ADVANCED HEALTHCARE MATERIALS Stinnett, G., Taheri, N., Villanova, J., Bohloul, A., Guo, X., Esposito, E. P., Xiao, Z., Stueber, D., Avendano, C., Decuzzi, P., Pautler, R. G., Colvin, V. L. 2021; 10 (11): e2001780


    Millions of people a year receive magnetic resonance imaging (MRI) contrast agents for the diagnosis of conditions as diverse as fatty liver disease and cancer. Gadolinium chelates, which provide preferred T1 contrast, are the current standard but face an uncertain future due to increasing concerns about their nephrogenic toxicity as well as poor performance in high-field MRI scanners. Gadolinium-containing nanocrystals are interesting alternatives as they bypass the kidneys and can offer the possibility of both intracellular accumulation and active targeting. Nanocrystal contrast performance is notably limited, however, as their organic coatings block water from close interactions with surface Gadoliniums. Here, these steric barriers to water exchange are minimized through shape engineering of plate-like nanocrystals that possess accessible Gadoliniums at their edges. Sulfonated surface polymers promote second-sphere relaxation processes that contribute remarkable contrast even at the highest fields (r1 = 32.6 × 10-3 m Gd-1 s-1 at 9.4 T). These noncytotoxic materials release no detectable free Gadolinium even under mild acidic conditions. They preferentially accumulate in the liver of mice with a circulation half-life 50% longer than commercial agents. These features allow these T1 MRI contrast agents to be applied for the first time to the ex vivo detection of nonalcoholic fatty liver disease in mice.

    View details for DOI 10.1002/adhm.202001780

    View details for Web of Science ID 000641909600001

    View details for PubMedID 33882196

  • Nanoparticle-Catalyzed Green Chemistry Synthesis of Polybenzoxazole JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Shen, M., Yu, C., Guan, H., Dong, X., Harris, C., Xiao, Z., Yin, Z., Muzzio, M., Lin, H., Robinson, J. R., Colvin, V. L., Sun, S. 2021; 143 (4): 2115-2122


    Enabling catalysts to promote multistep chemical reactions in a tandem fashion is an exciting new direction for the green chemistry synthesis of materials. Nanoparticle (NP) catalysts are particularly well suited for tandem reactions due to the diverse surface-active sites they offer. Here, we report that AuPd alloy NPs, especially 3.7 nm Au42Pd58 NPs, catalyze one-pot reactions of formic acid, diisopropoxy-dinitrobenzene, and terephthalaldehyde, yielding a very pure thermoplastic rigid-rod polymer, polybenzoxazole (PBO), with a molecular weight that is tunable from 5.8 to 19.1 kDa. The PBO films are more resistant to hydrolysis and possess thermal and mechanical properties that are superior to those of commercial PBO, Zylon. Cu NPs are also active in catalyzing tandem reactions to form PBO when formic acid is replaced with ammonia borane. Our work demonstrates a general approach to the green chemistry synthesis of rigid-rod polymers as lightweight structural materials for broad thermomechanical applications.

    View details for DOI 10.1021/jacs.0c12488

    View details for Web of Science ID 000618171900048

    View details for PubMedID 33493397

  • Libraries of Uniform Magnetic Multicore Nanoparticles with Tunable Dimensions for Biomedical and Photonic Applications ACS APPLIED MATERIALS & INTERFACES Xiao, Z., Zhang, Q., Guo, X., Villanova, J., Hu, Y., Kulaots, I., Garcia-Rojas, D., Guo, W., Colvin, V. L. 2020; 12 (37): 41932-41941


    Multicore iron oxide nanoparticles, also known as colloidal nanocrystal clusters, are magnetic materials with diverse applications in biomedicine and photonics. Here, we examine how both of their characteristic dimensional features, the primary particle and sub-micron colloid diameters, influence their magnetic properties and performance in two different applications. The characterization of these basic size-dependent properties is enabled by a synthetic strategy that provides independent control over both the primary nanocrystal and cluster dimensions. Over a wide range of conditions, electron microscopy and X-ray diffraction reveal that the oriented attachment of smaller nanocrystals results in their crystallographic alignment throughout the entire superstructure. We apply a sulfonated polymer with high charge density to prevent cluster aggregation and conjugate molecular dyes to particle surfaces so as to visualize their collection using handheld magnets. These libraries of colloidal clusters, indexed both by primary nanocrystal dimension (dp) and overall cluster diameter (Dc), form magnetic photonic crystals with relatively weak size-dependent properties. In contrast, their performance as MRI T2 contrast agents is highly sensitive to cluster diameter, not primary particle size, and is optimized for materials of 50 nm diameter (r2 = 364 mM-1 s-1). These results exemplify the relevance of dimensional control in developing applications for these versatile materials.

    View details for DOI 10.1021/acsami.0c09778

    View details for Web of Science ID 000572965700099

    View details for PubMedID 32812740

  • Homogeneously Dispersed Co9S8 Anchored on Nitrogen and Sulfur Co-Doped Carbon Derived from Soybean as Bifunctional Oxygen Electrocatalysts and Supercapacitors ACS APPLIED MATERIALS & INTERFACES Xiao, Z., Xiao, G., Shi, M., Zhu, Y. 2018; 10 (19): 16436-16448


    Developing low-cost and highly active multifunctional electrocatalysts to replace noble metal catalysts is crucial for the commercialization of future clean energy technology. Herein, homogeneous Co9S8 nanoparticles anchored on nitrogen and sulfur co-doped porous carbon nanomaterials (CoS@NSCs) are fabricated by pyrolysis of natural soybean treated with cobalt nitrate. The unique porous structures of the soybean are utilized to provide space for the oxidation and complexation reactions for cobalt compounds, thus leading to in situ generation of homogenously dispersed cobalt sulfide nanoparticles that anchored on the N,S co-doped carbon framework. Because of the coupling effect of cobalt sulfide and doping heteroatoms, CoS@NSC-800 not only displays excellent electrocatalytic performances with low overpotential and high current density toward both oxygen reduction reaction and oxygen evolution reaction comparable to the commercial Pt/C catalyst and IrO2 catalyst, but also might be a promising candidate for high-performance supercapacitors. The method for the preparation of the multifunctional hybrids is simple but effective for the formation of uniformly distributed metal sulfide nanoparticles anchored on carbon materials, therefore providing a new perspective for the design and synthesis of multifunctional electrocatalysts for electrochemical energy conversion and storage at a large scale.

    View details for DOI 10.1021/acsami.8b01592

    View details for Web of Science ID 000432753800024

    View details for PubMedID 29613758

  • Natural tea-leaf-derived, ternary-doped 3D porous carbon as a high-performance electrocatalyst for the oxygen reduction reaction NANO RESEARCH Guo, Z., Xiao, Z., Ren, G., Xiao, G., Zhu, Y., Dai, L., Jiang, L. 2016; 9 (5): 1244-1255
  • China rose-derived tri-heteroatom co-doped porous carbon as an efficient electrocatalysts for oxygen reduction reaction RSC ADVANCES Xiao, Z., Gao, X., Shi, M., Ren, G., Xiao, G., Zhu, Y., Jiang, L. 2016; 6 (89): 86401-86409

    View details for DOI 10.1039/c6ra14619h

    View details for Web of Science ID 000384322700085