A Multiplex "Disposable Photonics" Biosensor Platform and Its Application to Antibody Profiling in Upper Respiratory Disease

Photonic technologies promise to deliver quantitative, multiplex, and inexpensive medical diagnostic platforms by leveraging the highly scalable processes developed for the fabrication of semiconductor microchips. However, in practice, the affordability of these platforms is limited by complex and expensive sample handling and optical alignment. We previously reported the development of a disposable photonic assay that incorporates inexpensive plastic micropillar microfluidic cards for sample delivery. That system as developed was limited to singleplex assays due to its optical configuration. To enable multiplexing, we report a new approach addressing multiplex light I/O, in which the outputs of individual grating couplers on a photonic chip are mapped to fibers in a fiber bundle. As demonstrated in the context of detecting antibody responses to influenza and SARS-CoV-2 antigens in human serum and saliva, this enables multiplexing in an inexpensive, disposable, and compact format.

Interfacing neural cells with typical microelectronics materials for future manufacturing

The biocompatibility of materials used in electronic devices is critical for the development of implantable devices like pacemakers and neuroprosthetics, as well as in future biomanufacturing. Biocompatibility refers to the ability of these materials to interact with living cells and tissues without causing an adverse response. Therefore, it is essential to evaluate the biocompatibility of metals and semiconductor materials used in electronic devices to ensure their safe use in medical applications. Here, we evaluated the biocompatibility of a collection of diced silicon chips coated with a variety of metal thin films, interfacing them with different cell types, including murine mastocytoma cells in suspension culture, adherent NIH 3T3 fibroblasts, and human induced pluripotent stem cell (iPSC)-derived neural progenitor cells (NPCs). All materials tested were biocompatible and showed the potential to support neural differentiation of iPSC-NPCs, creating an opportunity to use these materials in a scalable production of a range of biohybrid devices such as electronic devices to study neural behaviors and neuropathies.

Highly Sensitive Fentanyl Detection Based on Nanoporous Electrochemical Immunosensors

Rapid and accurate detection of fentanyl (highly potent opioid) is a critical importance due to current opioids crisis worldwide. We report the highly sensitive detection of fentanyl utilizing the synergetic effect of nanoporous silicon as a substrate with a high interfacial area and specific antibody functionalization of nanoporous silicon. The electrochemical sensor consists of gold working and counter electrodes deposited on nanoprous silicon, antibodies immobilized between these electrodes and an Ag/AgCl reference electrode. Square wave voltammetry was used as an electrochemical transduction method. The detection limit was determined as 6 ng/ml and 11.5 ng/ml for specific peak (fentanyl signature) in phosphate buffer and human sweat, respectively. A future goal of this study is to a wearable sweat sensor array for rapid and on-site detection of multiple opioids with analytical sensitivity comparable with laboratory tests.

Lithographically patterned micro-nozzles for controlling fluid flow profiles for drug delivery and in vitro imaging applications

Precisely controlling delivery of drugs and other reagents is important for intravital microscopy studies. In this work, photolithographic integration of micro-nozzles onto a microfluidic platform was performed to tune the fluid flow profile and depth of penetration into biological tissue mimics. Performance characteristics were measured by correlating the flow rate through the device to the applied pressure and/or delivery of dyes into solution and agarose gel-based phantom tissue. From these results, the implementation of micro-nozzles was demonstrated to significantly improve the lateral dispersion of delivered fluid and increase the depth of penetration into phantom tissue.

Disposable photonics for cost-effective clinical bioassays: application to COVID-19 antibody testing

Decades of research have shown that biosensors using photonic circuits fabricated using CMOS processes can be highly sensitive, selective, and quantitative. Unfortunately, the cost of these sensors combined with the complexity of sample handling systems has limited the use of such sensors in clinical diagnostics. We present a new "disposable photonics" sensor platform in which rice-sized (1 × 4 mm) silicon nitride ring resonator sensor chips are paired with plastic micropillar fluidic cards for sample handling and optical detection. We demonstrate the utility of the platform in the context of detecting human antibodies to SARS-CoV-2, both in convalescent COVID-19 patients and for subjects undergoing vaccination. Given its ability to provide quantitative data on human samples in a simple, low-cost single-use format, we anticipate that this platform will find broad utility in clinical diagnostics for a broad range of assays.

Multiplexed detection and quantification of human antibody response to COVID-19 infection using a plasmon enhanced biosensor platform

The 2019 SARS CoV-2 (COVID-19) pandemic has illustrated the need for rapid and accurate diagnostic tests. In this work, a multiplexed grating-coupled fluorescent plasmonics (GC-FP) biosensor platform was used to rapidly and accurately measure antibodies against COVID-19 in human blood serum and dried blood spot samples. The GC-FP platform measures antibody-antigen binding interactions for multiple targets in a single sample, and has 100% selectivity and sensitivity (n = 23) when measuring serum IgG levels against three COVID-19 antigens (spike S1, spike S1S2, and the nucleocapsid protein). The GC-FP platform yielded a quantitative, linear response for serum samples diluted to as low as 1:1600 dilution. Test results were highly correlated with two commercial COVID-19 antibody tests, including an enzyme linked immunosorbent assay (ELISA) and a Luminex-based microsphere immunoassay. To demonstrate test efficacy with other sample matrices, dried blood spot samples (n = 63) were obtained and evaluated with GC-FP, yielding 100% selectivity and 86.7% sensitivity for diagnosing prior COVID-19 infection. The test was also evaluated for detection of multiple immunoglobulin isotypes, with successful detection of IgM, IgG and IgA antibody-antigen interactions. Last, a machine learning approach was developed to accurately score patient samples for prior COVID-19 infection, using antibody binding data for all three COVID-19 antigens used in the test.

A Dynamic Culture Method to Produce Ovarian Cancer Spheroids under Physiologically-Relevant Shear Stress

The transcoelomic metastasis pathway is an alternative to traditional lymphatic/hematogenic metastasis. It is most frequently observed in ovarian cancer, though it has been documented in colon and gastric cancers as well. In transcoelomic metastasis, primary tumor cells are released into the abdominal cavity and form cell aggregates known as spheroids. These spheroids travel through the peritoneal fluid and implant at secondary sites, leading to the formation of new tumor lesions in the peritoneal lining and the organs in the cavity. Models of this process that incorporate the fluid shear stress (FSS) experienced by these spheroids are few, and most have not been fully characterized. Proposed herein is the adaption of a known dynamic cell culture system, the orbital shaker, to create an environment with physiologically-relevant FSS for spheroid formation. Experimental conditions (rotation speed, well size and cell density) were optimized to achieve physiologically-relevant FSS while facilitating the formation of spheroids that are also of a physiologically-relevant size. The FSS improves the roundness and size consistency of spheroids versus equivalent static methods and are even comparable to established high-throughput arrays, while maintaining nearly equivalent viability. This effect was seen in both highly metastatic and modestly metastatic cell lines. The spheroids generated using this technique were fully amenable to functional assays and will allow for better characterization of FSS's effects on metastatic behavior and serve as a drug screening platform. This model can also be built upon in the future by adding more aspects of the peritoneal microenvironment, further enhancing its in vivo relevance.

Self-Balancing Position-Sensitive Detector (SBPSD)

Optical position-sensitive detectors (PSDs) are a non-contact method of tracking the location of a light spot. Silicon-based versions of such sensors are fabricated with standard CMOS technology, are inexpensive and provide a real-time, analog signal output corresponding to the position of the light spot. An innovative type of optical position sensor was developed using two back-to-back connected photodiodes. These so called self-balancing position-sensitive detectors (SBPSDs) eliminate the need for external readout circuitry entirely. Fabricated prototype devices demonstrate linear, symmetric coordinate characteristics and a spatial resolution of 200 μm for a 74 mm device. PSDs are commercially available only up to a length of 37 mm. Prototype devices were fabricated with various lengths up to 100 mm and can be scaled down to any size below that.

A Systematic Study of the Formation of Nano-Tips on Silicon Thin Films by Excimer Laser Irradiation

Recently, we reported conditions for controllable, direct laser fabrication of sharp conical tips with heights of about one micrometer and apical radii of curvature of several tens of nanometers. An individual cone is formed when a single-crystal silicon film on an insulator substrate is irradiated in air environment with a single pulse from a KrF excimer laser, homogenized and shaped to a circular spot several microns in diameter. In this work, we present a study of the formation of such tips as a function of the laser fluence, the film thickness, and the diameter of the irradiated spot. Atomic force microscopy and scanning electron microscopy were used to study the topography of the structures. A simple mechanism of formation based on movement of melted material is proposed. We have also studied structures (nano-ridges) that resulted from irradiation with narrow lines (width of several microns) instead of circular spots.

A living cell-based biosensor utilizing G-protein coupled receptors: principles and detection methods

This study explores the feasibility of using a bullfrog fibroblast cell line (FT cells) expressing G protein coupled receptors (GPCRs) as the basis for a living cell-based biosensor. We have fabricated gold microelectrode arrays on a silicon dioxide substrate that supports long term, robust growth of the cells at room temperature and under ambient atmospheric conditions. Activation of an endogenous GPCR to ATP was monitored with an optical method that detects rises in intracellular calcium and with an electrochemical method that monitors the increased secretion of pre-loaded norepinephrine on a MEMS device. FT cells were also transfected to express reporter genes driven by several different promoters, raising the possibility that they could be modified genetically to express novel GPCRs as well. The ability to harness GPCRs for BioMEMS applications by using cells that are easy to grow on MEMS devices and to modify genetically opens the way for a new generation of devices based on these naturally selective and highly sensitive chemoreceptors.

Amperometric detection of quantal catecholamine secretion from individual cells on micromachined silicon chips

We have fabricated electrochemical electrodes in picolitersized wells for measuring catecholamine release from individual cells with millisecond resolution. Each well-electrode roughly conforms to the shape of the cell in order to capture a large fraction of released catecholamine with high time resolution. Using this device, we can resolve spikes in amperometric current corresponding to quantal catecholamine release via exocytosis. In addition, we have combined amperometric recording on the chip with patch-clamp recordings of membrane capacitance as an assay of exocytosis. A quantitative comparison of the two methods suggests that a large fraction of catecholamine release is oxidized on the surface of the well-electrode. This technology has applications in cell-based biosensor development, high-throughput screening of drugs, and basic science investigations.