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Multidomain-Based Responsive Materials with Dual-Mode Optical Readouts
You, Yil-Hwan,Biswas, Aniket,Nagaraja, Ashvin T.,Hwang, Jin-Ha,Coté,, Gerard L.,McShane, Michael J. American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.15
<P>Responsive materials designed to generate signals for both surface-enhanced Raman spectroscopy (SERS) and phosphorescence lifetime-“dual-mode”-measurements are described. To demonstrate this concept, we incorporated pH-sensitive and oxygen-sensitive microdomains into a single hydrogel that could be interrogated via SERS and phosphorescence lifetime, respectively. Microdomains consisted two populations of discrete microcapsules containing either (1) gold nanoparticles capped with pH-sensitive Raman molecules or (2) oxygen-sensitive benzoporphyrin phosphors. While the microdomain-embedded hydrogels presented an expected background luminescence, the pH-sensitive SERS signal was distinguishable for all tested conditions. Response characteristics of the dual sensor showed no significant difference when compared to standalone single-mode pH and oxygen sensors. In addition, the feasibility of redundant multimode sensing was proven by observing the reaction produced by glucose oxidase chemically cross-linked within the corresponding alginate matrix. Each optical mode showed a signal change proportional to glucose concentration with an opposite signal directionality. These results support the promise of micro-/nanocomposite materials to improve measurement accuracy using intrinsic multimode responses and built-in redundancy, concepts that have broad appeal in the chemical sensing and biosensing fields.</P> [FIG OMISSION]</BR>
SERS-Active Smart Hydrogels With Modular Microdomains: From pH to Glucose Sensing
You, Yil-Hwan,Nagaraja, Ashvin T.,Biswas, Aniket,Hwang, Jin-Ha,Cote, Gerard L.,McShane, Michael J. IEEE 2017 IEEE SENSORS JOURNAL Vol.17 No.4
<P>A sensing hydrogel was demonstrated using pH-sensitive surface-enhanced Raman scattering (SERS) reporters embedded in modular microdomains. The gold nanoparticle-based pH probes capped with 4-mercaptobenzonic acid (MBA-AuNPs) were encapsulated within polyelectrolyte multilayer microcapsules within a surrounding hydrogel matrix. The materials were fully characterized for pH sensitivity and reproducibility of Raman scattering, which revealed low background (hydrogel) signals and a sigmoidal response curve for ratiometric intensity changes at 1430 and 1078 cm(-1), respectively. The analytical range was pH 4.43-8.07 (pKa similar to 5.80) with an average sensitivity of 0.07 pH-1. To assess the potential for sensing enzymatic substrates, hydrogels were prepared with the MBA-AuNPs co-encapsulated with glucose oxidase. Raman spectra recorded from hydrogels exposed to physiological glucose levels (0-400 mg/dL) exhibited apparent trends of decreasing pH from pH similar to 6.50 to pH similar to 4.50 due to glucose oxidization within the microdomains. The glucose diffusion into the capsules was controlled by crosslinking the polyelectrolyte multilayers with glutaraldehyde, showing an approach to adjust the balance of oxygen and glucose flux into the microcavities, yielding a tunable sensitivity of the glucose-proportional change at steady-state pH. These findings illustrate the potential of hydrogel hosts for a flexible approach to pseudo-solid-state SERS sensing devices for multiple small molecule targets.</P>