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Porous silicon (PSi)-based biosensors are a promising platform for quantitative rapid diagnostics, but they have not broadly realized clinically relevant limits of detection due, in part, to poor baseline stability. Baseline instability can be attributed to two major physicochemical challenges - hydrolysis of PSi in aqueous solutions and fouling by unwanted biological species, both of which can obscure the detection of target molecules at low concentrations. In this work, PSi was thermally hydrosilated with vinylbenzyl chloride (VBC) to incorporate hydrolytically stable Si−C bonding and to provide an attached alkyl halide termination for further chemistry. Subsequent grafting of zwitterionic poly(sulfobetaine methacrylate) (SBMA) from this PSi-VBC layer by surface-initiated atom-transfer radical polymerization (siATRP) formed an antifouling coating. Films both with and without the antifouling polymer were exposed to PBS (pH 7.4) and human blood serum, and optical reflectance measurements were used to monitor hydrolysis and nonspecific adsorption. PSi-VBC-polySBMA surfaces exhibited little to no nonspecific binding, as determined by ATR-FTIR and optical reflectance measurements, due to their hydrophilicity. The compatibility of hydrosilylation and siATRP with various chemical groups provides significant versatility in this surface chemistry approach, as well as facilitates the incorporation of highly specific capture agents. By directly addressing the issues of hydrolysis and fouling, this strategy holds promise for reducing the limits of detection in complex biological samples. 

A paper-based biosensor integrating a functionalized porous silicon (PSi) membrane as the active sensing element for quantifiable protein detection has been developed. For similar short-time exposures to an analyte, improved molecular transport in PSi membranes when on paper leads to larger signal changes compared to traditional PSi films that remain on a silicon substrate. In this work, we discuss controlling the incubation time of the analyte and the overall testing time of the sensor by incorporating different combinations of wicking and absorbent paper beneath the PSi membrane. With this control, the PSi-on-paper sensor platform has the potential to serve as an effective low-cost rapid diagnostic test with highly sensitive, quantitative readout for a wide range of analytes. 

Porous silicon (PSi) thin films on silicon substrates have been extensively investigated in the context of biosensing applications, particularly for achieving label-free optical detection of a wide range of analytes. However, mass transport challenges have made it difficult for these biosensors to achieve rapid response times and low detection limits. In this work, we introduce an approach for improving the efficiency of molecule transport in PSi by using open-ended PSi membranes atop paper substrates in a flow-through sensor scheme. The paper substrate provides structural support as well as an efficient means of draining solutions from the PSi membrane without the use of an external pump and microfluidic channels. Distinct changes in the reflectance properties of the PSi membrane are measured when molecules are captured in the membrane. A concentration dependent response of the sensor for protein detection is demonstrated. Factors influencing the interaction time of molecules in the PSi membrane and the drying time of the membrane, which directly affect the detection sensitivity and overall testing time, are discussed. The demonstrated performance of the PSi-on-paper sensor establishes the feasibility of a platform for low-cost rapid diagnostic tests with a highly sensitive, quantitative readout. 

We demonstrate higher sensitivity detection of proteins in a photonic crystal platform by including a deep subwavelength feature in the unit cell that locally increases the energy density of light. Through both simulations and experiments, the sensing capability of a deep subwavelength-engineered silicon antislot photonic crystal nanobeam (PhCNB) cavity is compared to that of a traditional PhCNB cavity. The redistribution and local enhancement of the energy density by the 50 nm antislot enables stronger light-molecule interaction at the surface of the antislot and leads to a larger resonance shift upon protein binding. This surface-based energy enhancement is confirmed by experiments demonstrating a nearly 50% larger resonance shift upon attachment of streptavidin molecules to biotin-functionalized antislot PhCNB cavities. 

We report a quantum-well-intermixing-free three-section mode-locked laser diode at 1580nm, featuring 1.70 psec pulse width. The fixed-point frequency analysis shows four different laser parameters conducive for compensating repetition rate and carrier frequency variations in space environment. 

We report a simple, vacuum-compatible fiber attach process forin situstudy of grating-coupled photonic devices. The robustness of this technique is demonstrated on grating-coupled waveguides exposed to multiple X-ray irradiations for aerospace studies. 

Perforated microelectrode arrays (pMEAs) have become essential tools for ex vivo retinal electrophysiological studies. pMEAs increase the nutrient supply to the explant and alleviate the accentuated curvature of the retina, allowing for long-term culture and intimate contacts between the retina and electrodes for electrophysiological measurements. However, commercial pMEAs are not compatible with in situ high-resolution optical imaging and lack the capability of controlling the local microenvironment, which are highly desirable features for relating function to anatomy and probing physiological and pathological mechanisms in retina. Here we report on microfluidic pMEAs (μpMEAs) that combine transparent graphene electrodes and the capability of locally delivering chemical stimulation. We demonstrate the potential of μpMEAs by measuring the electrical response of ganglion cells to locally delivered high K + stimulation under controlled microenvironments. Importantly, the capability for high-resolution confocal imaging of the retina tissue on top of the graphene electrodes allows for further analyses of the electrical signal source. The new capabilities provided by μpMEAs could allow for retinal electrophysiology assays to address key questions in retinal circuitry studies.