Fluorescent polystyrene (PS) nanobeads in the size range ∼70–120 nm incorporating perylene bisimide (PBI-PS) and/or oligo­(p-phenylenevinylene) (OPV-PS) was developed by miniemulsion polymerization technique. A dye loading content (DLC) of <3% was sufficient to impart high fluorescence emission capability to the PS beads. OPV-PS exhibited emission in the range 400–550 nm with peak emission at 450 nm (λex = 350 nm; ϕFL = 26%); PBI-PS showed emission from 520–650 nm with peak emission at 545 nm (λex = 490 nm; ϕFL = 9.7%) in 1× PBS buffer, whereas OPV­(PBI)-PS nanobeads incorporating both the fluorophores exhibited multicolor emission capabilities (λex from 350 to 490 nm). The nanoparticles were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and dynamic light scattering (DLS) for size and zeta potential for surface charge. For bioimaging applications, the PS nanoparticles were incubated with HeLa cells. Cell viability analysis involving HeLa cells showed more than 90% cell viability confirming the biocompatibility of the PS beads. The cellular uptake of the nanoparticles was confirmed by flow cytometry analysis and confocal laser scanning microscopy (CLSM) images. The subcellular localization of the nanoparticles in the cytoplasm could be precisely established by their simultaneous multicolor emission. The PS-based single optical agent presented here that can function as three-channel fluorescent probe to meet the requirements for multicolor bioimaging is advantageous.

Amphiphilic polystyrene having pendant glucuronic acid (PS-DGlu) was designed and systematically synthesized to be used as a stabilizing agent in styrene miniemulsion polymerization, while covalently incorporating oligo­(p-phenylenevinylene) (OPV)-based fluorophore to prepare PSG-OPV-n. This OPV fluorophore was incorporated with an aim to work as a signal transducer, while glucuronic acid on the surface of PS nanobeads would act as the water solubilizing moiety for PS to enable it to function as surfactant and also serve as an interaction site for free bilirubin to facilitate noncovalent interaction via hydrogen bonding. Efficient energy transfer from OPV to bilirubin was observed, owing to the appreciable spectral overlap between emission of OPV and absorption of bilirubin. Visual color change from blue to bluish green was observed under an UV lamp after the addition of bilirubin into the polymer. Selectivity of the sensor was checked among the pool of other interferences, such as glucose, sucrose, metal ions, cholesterol, and biliverdin. The limit of detection was found to be as low as 20 nM, which is far less than the clinical range for causing jaundice (<25 to >50 μmol/L). Moreover, the developed sensor showed its effectiveness toward real time monitoring of free bilirubin in human serum.

Solid state emitting, distinctly dual vapor sensors with high quantum yield was developed using polystyrene incorporating two fluorophores following a miniemulsion polymerization method. Selective functionalization with carboxy and amine functionality was used to decorate the resulting polystyrene nanobeads having both perylenebisimide (PBI) and oligo (p-phenylenevinylene) (OPV) fluorophores. These nanobeads with a size of 70−180 nm showed near white emission under UV light. On contact with vapors of specific electron deficient nitroaromatics OPV emission got selectively quenched to show yellow emission from the nanobeads under UV radiation. Exposure to amine vapor quashed PBI emission selectively resulting in blue emission under UV lamp. Such a vast range of color alteration from white to either blue or yellow from the same sensor makes it a true dual analyte sensor with two distinct outputs. Control of surface functionality (−COOH, −NH 2 , and neutral) on the nanobeads played a pivotal role in boosting the sensing efficiency; introduction of functionality on the surface facilitated analyte-sensor interaction through hydrogen bonding, prompting their fast responsiveness. Real time, potential device based application was demonstrated with free-standing films which was capable of efficient detection with fast analyte exchange from dilute solutions. Recyclability of the film sensor was demonstrated with 8 cycles of reuse.