We present a compact, cost-effective, label-free, real-time biosensor based on long-range surface plasmon polariton (LRSPP) gold (Au) waveguides for the detection of dengue-specific immunoglobulin M (IgM) antibody, and we demonstrate detection in actual patient blood plasma samples. Two surface functionalization approaches are proposed and demonstrated: a dengue virus serotype 2 (DENV-2) functionalized surface to capture dengue-specific IgM antibody in blood plasma and the reverse, a blood plasma functionalized surface to capture DENV-2. The results obtained via these two surface functionalization approaches are comparable to, or of greater quality, than those collected by conventional IgM antibody capture enzyme linked immunosorbent assay (MAC-ELISA). Our second functionalization approach was found to minimize nonspecific binding, thus improving the sensitivity and accuracy of the test. We also demonstrate reuse of the biosensors by regenerating the sensing surface down to the virus (or antibody) level or down to the bare Au.

Compact and smart optical gas sensors have attracted significant attention over the past few decades. Among the materials used for developing such gas sensors, group-IV materials, including silicon, germanium, carbon allotropes, and their compounds, are considered the most promising candidates. By virtue of their inherent compatibility with the CMOS fabrication process in the mature microelectronics industry, onchip optical gas sensors based on group-IV materials have merits of appreciable sensitivity and high-density integration. Moreover, such sensors have promising potential to be integrated with other electronic or photonic devices for on-chip signal processing and communication, which are expected to enable versatile applications in the internet of things, point-of-care testing, and information and communication technology. This paper is the review of basic principles, state-of-the-art devices, and cutting-edge applications of on-chip optical gas sensors based on group-IV materials and discussions of their prospects.

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