The properties of synthetically hydroxyapatites are significantly affected by chemical or radiological exposures making these materials good sensors. Since early sixties hydroxyapatites single crystals have been investigated for sensors and laser host applications. Hydroxyapatites are naturally occurring mineral calcium apatite with the formula Ca₅(PO₄)₆(OH)₂ . When the OH− ion is replaced by halides (F, Cl) and carbonate these are referred as haloapatites such as fluorapatite and chlorapatite. These materials generally belong to hexagonal symmetry. Most of the times naturally occurring apatite contain impurities and instead of transparent white these appear to be brown, green or yellow. Recently it has been realized that major portion of the body bone is some form of hydroxyapatite. We have studied several compositions of hydroxyapatites and synthesized by using nanoparticles of parent components and developed growth by sintering and grain growth. We observed that during grain growth hexagonal morphology is formed which changes to glassy phase depending on the cooling conditions and compositions.

We have grown several high atomic number and high density ternary single crystals for variety of sensors. These materials are layered compounds (also designated as 2D) and have shown great promise for radiation and optical sensors. For achieving the good quality single crystals thermal characteristics are required, we have characterized thallium lead iodide, thallium mercury iodide and thallium gallium selenide synthesized from binary thallium and mercury and lead salts. Both thermal gravimetric and differential thermal analysis was performed from 50 to 9000C using two systems including a PerkinElmer Pyris 1 TGA and platinum sample pan in the nitrogen atmosphere. We will compare these data with available phase diagram for the grown stoichiometric compound.

Plant pathogens represent a significant threat to food supplies. Agricultural diagnostics currently function on a paradigm involving either inaccurate visual inspection or burdensome laboratory molecular tests. Several field-ready diagnostic methods have been presented in recent years; however detection of pre-symptomatic or co-occurring infections and in-field sample processing remain challenges. To address these challenges, we developed surface-enhanced Raman scattering (SERS)-sensing hydrogels that uptake pathogenic material (RNA) and produce a measurable response on-site. Our novel reagentless SERS sensor for the detection of tobacco mosaic virus (TMV) was embedded in an environmentally compatible hydrogel material, to produce sensing hydrogels. We demonstrate the diagnostic application of our sensing hydrogels through exposure to TMV infected tobacco plants. This technology offers a field-deployable tool for pre-symptomatic and multiplexed molecular identification of pathogens with the potential to shift the current agricultural diagnostic paradigm.

The pandemic has shown that we need sensitive and deployable diagnostic technologies. Surface-enhanced Raman scattering (SERS) sensors can be an ideal solution for developing such advanced Point-of-Need (PON) diagnostic tests but their limitation is the achievable sensitivity, insufficient compared to what is needed for sensing of viral biomarkers. Noncovalent DNA catalysis mechanisms have been recently exploited for catalytic amplification in SERS assays. These advances used catalytic hairpin assembly (CHA) and other DNA self-assembly processes to develop sensing mechanisms with improved sensitivities. We developed and investigated a reagentless SERS sensing mechanism that uses catalytic amplification based on DNA self-assembly. We will discuss the design of this catalytic sensing mechanism and its automation into a design algorithm.

Point-of-sampling diagnostics has gained interest for its potential to detect trace amounts of analytes in real-time. Several challenges persist with developing accurate and reliable field-testing techniques, including limits of detection, portable and durable instrumentation, and cost effectiveness for routine monitoring. To combat these challenges, our goal is to develop a facile, field deployable Surface-Enhanced Raman Scattering (SERS) sensor for detecting trace amounts of Chemical Warfare Agents (CWAs) and environmental contaminants such as perfluoroalkyl substances (PFAS). In collaboration with the University of Cincinnati, we optimized the ink formulation and printing parameters for AgAu nanostars using a machine learning optimization algorithm to achieve the best SERS performance using the minimal AgAu nanostars. The SERS sensor performance and limits of detection were assessed using CWAs and PFAS. Future work includes exploring the tunability of the LSPR of the AgAu nanostars for compatibility with commercially available handheld Raman spectrometers.

Sandwich-based LFA device was successfully demonstrated to detect salivary lipopolysaccharides of P. gingivalis from human saliva. Although saliva is an attractive biofluid due to non-invasive sampling and excellent availability, isolating targeted biomarkers for analysis in saliva is challenging because of interferences from various biomolecules in saliva, especially by -amylase. Combined pre-treatment using potato starch and syringe filtration has been developed to reduce the interference from -amylase. Pretreated saliva presented a comparable LOD ~46 ng/mL with excellent selectivity versus other LPS and proteins. Future directions include not only the development of aptamer-based LFA but also adapting the Surface Enhanced Raman Scattering (SERS) technology for sensing target analytes in LFA in conjunction with novel silver-coated Au nanostar particles. Our prior research using aptamer in LFA and preliminary results of SERS detection in LFA will be presented to support our future directions.