Direct glucose sensing in the physiological range through plasmonic nanoparticle formation.

Development of improved glucose detection has vast significance in both clinical and point of care settings. Herein, we present a novel, label-free, enzyme-free, colorimetric method of glucose detection that relies on the reduction of a gold salt precursor facilitated by physiological concentrations of glucose (1.25-50 mM). The concentration of glucose present during the reduction process results in nanoparticles of different size, which in turn change the color of solution. Through transmission electron microscopy (TEM), it was found that the nanoparticle size decreases as the glucose concentration increases. Kinetic characterization of nanoparticle formation shows rate constants change 5-8 orders of magnitude when comparing normal versus diabetic glucose concentrations. Assay versatility was also investigated through incorporation onto solid substrates as well as the addition of a filtering step, which produced relatively clear samples below the diabetic cut-off (10 mM glucose) and colored samples above. The colorimetric sensor was then found to also show similar color changes with glucose solutions containing biological interfering agents as well as samples with 20% serum. Last, the sensor was tested in solution containing 100% mouse serum and 100% bovine urine spiked with varying glucose concentrations, which resulted in smaller nanoparticle formation whose intensities were dependent on glucose concentration. The resulting color changes observed for this sensor in urine samples are directly compared with Benedict's reagent and are shown to be significantly more sensitive to lower concentrations of glucose in the diabetic relevant range.