Robert Nidetz

Multiplex Serum Cytokine Immunoassay Using Nanoplasmonic Biosensor Microarrays

Precise monitoring of the rapidly changing immune status during the course of a disease requires multiplex analysis of cytokines from frequently sampled human blood. However, the current lack of rapid, multiplex, and low volume assays makes immune monitoring for clinical decision-making (e.g., critically ill patients) impractical. Without such assays, immune monitoring is even virtually impossible for infants and neonates with infectious diseases and/or immune mediated disorders as access to their blood in large quantities is prohibited. Localized surface plasmon resonance (LSPR)-based microfluidic optical biosensing is a promising approach to fill this technical gap as it could potentially permit real-time refractometric detection of biomolecular binding on a metallic nanoparticle surface and sensor miniaturization, both leading to rapid and sample-sparing analyte analysis. Despite this promise, practical implementation of such a microfluidic assay for cytokine biomarker detection in serum samples has not been established primarily due to the limited sensitivity of LSPR biosensing. Here, we developed a high-throughput, label-free, multiarrayed LSPR optical biosensor device with 480 nanoplasmonic sensing spots in microfluidic channel arrays and demonstrated parallel multiplex immunoassays of six cytokines in a complex serum matrix on a single device chip while overcoming technical limitations. The device was fabricated using easy-to-implement, one-step microfluidic patterning and antibody conjugation of gold nanorods (AuNRs). When scanning the scattering light intensity across the microarrays of AuNR ensembles with dark-field imaging optics, our LSPR biosensing technique allowed for high-sensitivity quantitative cytokine measurements at concentrations down to 5-20 pg/mL from a 1 μL serum sample. Using the nanoplasmonic biosensor microarray device, we demonstrated the ability to monitor the inflammatory responses of infants following cardiopulmonary bypass (CPB) surgery through tracking the time-course variations of their serum cytokines. The whole parallel on-chip assays, which involved the loading, incubation, and washing of samples and reagents, and 10-fold replicated multianalyte detection for each sample using the entire biosensor arrays, were completed within 40 min.

AC Electroosmosis-Enhanced Nanoplasmofluidic Detection of Ultralow-Concentration Cytokine

Label-free, nanoparticle-based plasmonic optical biosensing, combined with device miniaturization and microarray integration, has emerged as a promising approach for rapid, multiplexed biomolecular analysis. However, limited sensitivity prevents the wide use of such integrated label-free nanoplasmonic biosensors in clinical and life science applications where low-abundance biomolecule detection is needed. Here, we present a nanoplasmofluidic device integrated with microelectrodes for rapid, label-free analysis of a low-abundance cell signaling protein, detected by AC electroosmosis-enhanced localized surface plasmon resonance (ACE-LSPR) biofunctional nanoparticle imaging. The ACE-LSPR device is constructed using both bottom-up and top-down sensor fabrication methods, allowing the seamless integration of antibody-conjugated gold nanorod (AuNR) biosensor arrays with microelectrodes on the same microfluidic platform. Applying an AC voltage to microelectrodes while scanning the scattering light intensity variation of the AuNR biosensors results in significantly enhanced biosensing performance. The AC electroosmosis (ACEO) based enhancement of the biosensor performance enables rapid (5-15 min) quantification of IL-1β, a pro-inflammatory cytokine biomarker, with a sensitivity down to 158.5 fg/mL (9.1 fM) for spiked samples in PBS and 1 pg/mL (58 fM) for diluted human serum. Together with the optimized detection sensitivity and speed, our study presents the first critical step toward the application of nanoplasmonic biosensing technology to immune status monitoring guided by low-abundance cytokine measurement.

A fully automated portable gas chromatography system for sensitive and rapid quantification of volatile organic compounds in water

This paper presents the design, assembly and characterization of a fully automated portable gas chromatography system coupled with a purge-and-trap system for the sensitive and rapid field analysis of volatile organic compounds (VOCs) in water samples. The VOCs were firstly purged by helium gas in the micro-fabricated preconcentrator/injector and then injected into the downstream capillary column and photoionization detector for separation and detection. The purge-and-trap conditions were optimized to efficiently extract VOCs from water samples. The calibration of 6 VOCs with concentrations ranging from 1 μg L−1 to 500 μg L−1 showed excellent linearity (R2 > 0.99). Detection limits (3σ) of sub-μg L−1 (or sub-parts-per-billion level) were achieved, which are orders of magnitude lower than the maximum contaminant level (MCL) established by the US Environmental Protection Agency (EPA). The separation of 26 analytes (in a vapor pressure range from 0.087 Torr to 180 Torr) in a water sample in less than 15 minutes was also demonstrated. Finally, the optimized system was applied to field analysis of a groundwater sample in an environmental remediation site. The quantified results agreed well with those obtained by an analytical lab using standard analytical methods and instruments. Our system offers a lab-on-a-chip solution for sensitive and rapid water analysis compliant with the EPA sample collection method. It will have a wide range of applications in environmental monitoring, industries and healthcare.

Directed self-assembly of nanogold using a chemically modified nanopatterned surface

Electron-beam lithography (EBL) was used to define an aminosilane nanopatterned surface in order to electrostatically self-assemble gold nanoparticles (Au NPs). The chemically modified nanopatterned surfaces were immersed into a Au NP solution to allow the Au NPs to self-assemble. Equilibrium self-assembly was achieved in only 20 min. The number of Au NPs that self-assembled on an aminosilane dot was controlled by manipulating the diameters of both the Au NPs and the dots. Adding salt to the Au NP solution enabled the Au NPs to self-assemble in greater numbers on the same sized dot. However, the preparation of the Au NP solution containing salt was sensitive to spikes in the salt concentration. These spikes led to aggregation of the Au NPs and non-specific deposition of Au NPs on the substrate. The Au NP patterned surfaces were immersed in a sodium hydroxide solution in order to lift-off the patterned Au NPs, but no lift-off was observed without adequate physical agitation. The van der Waals forces are too strong to allow for lift-off despite the absence of electrostatic forces.

Fully Automated Portable Comprehensive 2-Dimensional Gas Chromatography Device

We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension (2D) to increase the 2D separation time (up to 32 s) and hence 2D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the 1D column to monitor the eluent from 1D and assist in reconstructing 1D elution peaks. With the information obtained jointly from the 1D and 2D detectors, 1D elution peaks could be reconstructed with significantly improved 1D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct 1D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C6-C12), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.

Low-Power Miniaturized Helium Dielectric Barrier Discharge Photoionization Detectors for Highly Sensitive Vapor Detection

This paper presents the design, fabrication, and characterization of a microhelium dielectric barrier discharge photoionization detector (μHDBD-PID) on chip with dimensions of only ∼15 mm × ∼10 mm × ∼0.7 mm and weight of only ∼0.25 g. It offers low power consumption (<400 mW), low helium consumption (5.8 mL/min), rapid response (up to ∼60 ms at a flow rate of 1.5 mL/min), quick warm-up time (∼5 min), an excellent detection limit (a few picograms), a large linear dynamic range (>4 orders of magnitude), and maintenance-free operation. Furthermore, the μHDBD-PID can be driven with a miniaturized (∼5 cm × ∼2.5 cm × ∼2.5 cm), light (22 g), and low cost (∼

Efficient molecular evolution to generate enantioselective enzymes using a dual-channel microfluidic droplet screening platform

2) power supply with only 1.5 VDC input. The dependence of the μHDBD-PID performance on bias voltage, auxiliary helium flow rate, carrier gas flow rate, and temperature was also systematically investigated. Finally, the μHDBD-PID was employed to detect permanent gases and a sublist of the EPA 8260 standard reagents that include 51 analytes. The μHDBD-PID developed here can have a broad range of applications in portable and microgas chromatography systems for in situ, real-time, and sensitive gas analysis.

Portable multi-dimensional gas chromatography device for rapid field analysis of chemical compounds

Directed evolution has long been a key strategy to generate enzymes with desired properties like high selectivity, but experimental barriers and analytical costs of screening enormous mutant libraries have limited such efforts. Here, we describe an ultrahigh-throughput dual-channel microfluidic droplet screening system that can be used to screen up to ~107 enzyme variants per day. As an example case, we use the system to engineer the enantioselectivity of an esterase to preferentially produce desired enantiomers of profens, an important class of anti-inflammatory drugs. Using two types of screening working modes over the course of five rounds of directed evolution, we identify (from among 5 million mutants) a variant with 700-fold improved enantioselectivity for the desired (S)-profens. We thus demonstrate that this screening platform can be used to rapidly generate enzymes with desired enzymatic properties like enantiospecificity, chemospecificity, and regiospecificity.Optimizing an enzyme usually requires testing thousands of variants, thus consuming large amounts of material and time. Here, the authors present a method that allows for measuring two different activities of the same enzyme simultaneously instead of doing two consecutive rounds of screening.

Microscale Gas Chromatography with Microsensor Array Detection: Challenges and Prospects

We report the progress made in the past few years in the development of a high performance portable multi-dimensional gas chromatography (GC) device that is capable of rapidly analyzing a large number of compounds with high sensitivity. We discuss the multi-dimensional GC architecture and its components, followed by a few field analysis examples using our portable GC devices.

Flow-through microfluidic photoionization detectors for rapid and highly sensitive vapor detection

The capability to analyze complex mixtures of airborne volatile organic compounds (VOCs) at low concentrations; in situ; has implications for environmental monitoring; worker exposure assessment; biomedical diagnostics; and population security. Since standalone microsensor arrays lack this capability; upstream separation of mixture components; often preceded by preconcentration; is required. Although significant advances have been made via MEMS technologies in the development of microscale gas chromatographic (μGC) systems; many challenges remain. This presentation will review selected aspects of the state-of-the-art in μGC for VOC mixture analysis. Here; we emphasize our progress toward a wearable μGC prototype.