Miniaturization overcomes macro sample analysis limitations: Salicylate-selective polystyrene nanoparticle-modified optical sensor.

Salicylate-selective polystyrene micro-optode is engineered using a mixed solvent method. The size of the particles (200-400 nm) and the distribution of the recognition components onto their surface were elucidated by transmission electron microscope and confocal fluorescence microscope. The polystyrene micro/nanoparticles are modified with thiourea derivative as ionophore, ETH 7075 as chromoionophore, and tridodecylmethyl ammonium chloride (TDMAC) as ion-exchanger. The response mechanism depends on the selective binding of the ionophore at the surface of the particles to salicylate. A concomitant protonation of the chromoionophore results in a decrease in the absorbance at the maximum wavelength, 535 nm. Enabling this sensing interaction at the micro-scale decreases the response time of the optode to be lower than 10 s the concentration range of 3-70 µM, with a detection limit of 2.1 μM. This microsphere sensing platform demonstrated excellent performance in the determination of salicylate in spiked urine samples and in pharmaceutical formulations. Further miniaturization of these micro-optodes promises in-vivo analysis of intracellular analytes.