The escalating research interests in porous media microfluidics, such as microfluidic paper-based analytical devices, have fostered a new spectrum of biomedical devices for point-of-care (POC) diagnosis and biosensing. In this paper, we report microfluidic diatomite analytical devices (μDADs), which consist of highly porous photonic crystal biosilica channels, as an innovative lab-on-a-chip platform to detect illicit drugs. The μDADs in this work are fabricated by spin-coating and tape-stripping diatomaceous earth on regular glass slides with cross section of 400×30µm. As the most unique feature, our μDADs can simultaneously perform on-chip chromatography to separate small molecules from complex biofluidic samples and acquire the surface-enhanced Raman scattering spectra of the target chemicals with high specificity. Owing to the ultra-small dimension of the diatomite microfluidic channels and the photonic crystal effect from the fossilized diatom frustules, we demonstrate unprecedented sensitivity down to part-per-billion (ppb) level when detecting pyrene (1ppb) from mixed sample with Raman dye and cocaine (10 ppb) from human plasma. This pioneering work proves the exclusive advantage of μDADs as emerging microfluidic devices for chemical and biomedical sensing, especially for POC drug screening.

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Surface-enhanced infrared absorption (SEIRA) is capable of identifying molecular fingerprints by resonant detection of infrared vibrational modes through the coupling with plasmonic modes of metallic nanostructures. However, SEIRA for on-chip gas sensing is still not very successful due to the intrinsically weak light-matter interaction between photons and gas molecules and the technical challenges in accumulating sufficient gas species in the vicinity of the spatially localized enhanced electric field, namely, the "hot-spots", generated through plasmonics. In this paper, we present a suspended silicon nitride (SiN) nanomembrane device by integrating plasmonic nanopatch gold antennas with metal-organic framework (MOF), which can largely adsorb carbon dioxide (CO) through its nanoporous structure. Unlike conventional SEIRA sensing relying on highly localized hot-spots of plasmonic nanoantennas or nanoparticles, the device reported in this paper engineered the coupled surface plasmon polaritons in the metal-SiN and metal-MOF interfaces to achieve strong optical field enhancement across the entire MOF film. We successfully demonstrated on-chip gas sensing of CO with more than 1800× enhancement factors by combining the concentration effect from the 2.7 μm MOF thin film and the optical field enhancement of the plasmonic nanopatch antennas.

A facile method to synthesize flower-like gold nanostructures showing multiple tips with dendritic structures is developed through a one-step reduction of HAuCl 4 with dopamine at room temperature. The gold nanoflowers clearly increase the surface enhanced Raman scattering (SERS) effect, demonstrate promising biocompatibility, and could be internalized by cancer cells, indicating their potential for biomedical applications.

We demonstrate a photonic crystal biosilica surface-enhanced Raman scattering (SERS) substrate based on a diatom frustule with in-situ synthesized silver nanoparticles (Ag NPs) to detect explosive molecules from nanoliter (nL) solution. By integrating high density Ag NPs inside the nanopores of diatom biosilica, which is not achievable by traditional self-assembly techniques, we obtained ultra-high SERS sensitivity due to dual enhancement mechanisms. First, the hybrid plasmonic-photonic crystal biosilica with three dimensional morphologies was obtained by electroless-deposited Ag seeds at nanometer sized diatom frustule surface, which provides high density hot spots as well as strongly coupled optical resonances with the photonic crystal structure of diatom frustules. Second, we discovered that the evaporation-driven microscopic flow combined with the strong hydrophilic surface of diatom frustules is capable of concentrating the analyte molecules, which offers a simple yet effective mechanism to accelerate the mass transport into the SERS substrate. Using the inkjet printing technology, we are able to deliver multiple 100 pico-liter (pL) volume droplets with pinpoint accuracy into a single diatom frustule with dimension around 30 μm × 7 μm × 5 μm, which allows for label-free detection of explosive molecules such as trinitrotoluene (TNT) down to 10−10 M in concentration and 2.7 × 10−15 g in mass from 120 nL solution. Our research illustrates a new paradigm of SERS sensing to detect trace level of chemical compounds from minimum volume of analyte using nature created photonic crystal biosilica materials.

Combined plasmonic nanocrystals and metal–organic framework thin-films are fabricated for sensing gases in the near-infrared range.

In this paper, we report a fiber-optic carbon dioxide (CO 2 ) near-infrared (IR) absorption sensor with only 8-cm sensing length that is coated with nanoporous metalorganic framework material Cu-BTC (BTC = benzene-1,3, 5-tricarboxylate). The multimode optical fiber was etched by hydrofluoric acid to remove the cladding and part of the core, resulting in larger evanescent field to sense the near-IR absorption induced by the adsorbed CO 2 . The Cu-BTC thin film with 100 nm thickness was then grown onto the ethced core through a stepwise layer-by-layer method. Our real-time measurement results show that the CO 2 detection limit is better than 500 ppm and the overall response time is 40 s for absorption and 75 s for desorption. To the best of our knowledge, this is the shortest near-IR fiber-optic sensor for CO 2 detection at 1.57-µm wavelength.Index Terms-Fiber optic sensor, gas sensor, near infrared absorption, metal-organic framework.

In this letter, we present a nanophotonic device consisting of plasmonic nanopatch array (NPA) with integrated metal-organic framework (MOF) for enhanced infrared absorption gas sensing. By designing a gold NPA on a sapphire substrate, we are able to achieve enhanced optical field that spatially overlaps with the MOF layer, which can adsorb carbon dioxide (CO) with high capacity. Experimental results show that this hybrid plasmonic-MOF device can effectively increase the infrared absorption path of on-chip gas sensors by more than 1100-fold. The demonstration of infrared absorption spectroscopy of CO using the hybrid plasmonic-MOF device proves a promising strategy for future on-chip gas sensing with ultra-compact size.