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We present a new composite material composed of pH sensitive fluorescent dyes in a poly(N-isopropylacrylamide)-based hydrogel and incorporating glucose oxidase (GOx), which provides a platform for fluorescence sensing of glucose in the clinically relevant range of 100 μM to 100 mM in aqueous solution. Fluorescein and rhodamine B dyes are well known for their dramatic pH-responsive changes in fluorescence emission color, in which they were introduced to the hydrogel as comonomers. As D-glucose was oxidized to D-glucono-δ-lactone producing hydrogen peroxide and a proton through the enzymatic action of GOx, the generated proton affects the fluorescence of the composite hydrogel. The composite hydrogel exhibited high selectivity to glucose over other sugars and metal ions. The combined role of a soft hydrogel and oxidase highlights the potential of the new composite material design for selective detection of glucose in aqueous solution.

We have synthesized a highly pH and temperature-sensitive, fluorescent, crosslinked poly(N-isopropylacrylamide) (PNIPAM)-based probe via simple free radical emulsion copolymerization, which formed a reversible microgel containing both fluorophores of fluorescein and rhodamine derivatives. We confirmed that the opening of the lactone ring of fluorescein and the lactam ring of rhodamine in the polymer was responsible for the fluorescence changes in basic and acidic conditions, which showed fluorescence emissions at 514 nm (green) and 586 nm (red), respectively. The polymeric microgel exhibited a linear relationship between the ratio of emission intensity and pH windows of pH 2–6 and 7–12. Moreover, the microgel exhibited changes in fluorescence intensity with an alteration of turbidity of the microgel induced by temperature. Moreover, these fluorescence changes could be easily observed by the naked eye, serving as a potential probe for ratiometric microgel detection of pH or temperature.

Fluorescent conjugated polymers with various monomer compositions were synthesized via Suzuki coupling polymerization and spherically-shaped conjugated polymer dots (CPdot) with uniform size were prepared via conventional reprecipitation technique. Chemically modified graphene oxide (GO) was prepared to use as a component of sensor platform for protein detection. GO showed an excellent interaction with CPdot on its surface via hydrophobic interaction, which, in turn, induced the quenching of the fluorescence of CPdot. Upon exposure to bovine serum albumin (BSA), the quenched fluorescence was recovered, resulting from the release of CPdot from the complex with GO, as BSA adsorbed preferentially on the GO surface.

Fluorescent 3′,6′-bis(octyloxy)-p-terphenyl-4,4′-dialdehyde 3 has been successfully synthesized via a Suzuki cross-coupling reaction of the corresponding dibromo compound with a boronic acid compound in the presence of palladium catalyst. The fluorescent probe molecule has aldehyde groups at both ends, which can be used as reactive sites for amines. Alteration of emission is expected by an interaction of 3 with amines, specifically ethylenediamine, which can be a measure of amine concentration. Moreover, uniform-sized poly(methyl methacrylate) (PMMA) particles were prepared to use as a probe matrix and 3 was incorporated in the PMMA particles during dispersion polymerization, which can be a sensitive and selective sensor platform for ethylenediamine.

A turn-on fluorescent probe, based on a water-soluble terphenyl derivative, for the detection of cysteine and homocysteine is reported. The aldehyde groups in the probe play crucial roles in providing reaction with thiol groups in the amino acids, leading to a formation of thiazolidine (from cysteine) or thiazinane ring (from homocysteine). As a result, the new formation of such rings alters the electronic property of the conjugated system in the probe and results in emission enhancement. The probe in aqueous solution exhibits a remarkable increase in its quantum yield upon exposure to cysteine (up to 20-fold) and to homocysteine (up to 700-fold), while slight quenching is observed in the presence of glutathione. Moreover, an investigation on time-resolved fluorescence spectra of the probe in the presence of cysteine and homocysteine reveals potential discriminatory detection of cysteine and homocysteine. Bioimaging of the thiols in live HeLa cells was successfully applied.

Conjugated polymer of poly(fluorene-co-quinoxaline) was synthesized via Suzuki coupling polymerization. The emission color of the polymer can be tuned depending on the concentration of the polymer in solution. A low-energy bandgap is observed both in the concentrated solution and in the solid state, caused by aggregation of the polymer chains, resulting in long wavelength emission from the quinoxaline moiety, while short wavelength emission can be seen in diluted, well-dissolved solution. The presence of quinoxaline units enables us to demonstrate fluorescence switching and imaging. Paper-based strips containing the polymer are prepared via simple immersion of filter paper in the polymer solution for practical use in the detection of nerve agents. The emission of the paper-based strip is quenched upon exposure to diethyl chlorophosphate (DCP), a nerve agent simulant, and the initial emission intensity can be almost restored by treatment with aqueous sodium hydroxide solution, making a possible reversible paper-based sensor.