A Long Wavelength Fluorescent Hydrophilic Copolymer Based on Naphthalenediimide as pH Sensor with Broad Linear Response Range

Successful operation of a microbioreactor is dependent upon the monitoring and control of pH in culture fluids. Introducing chemosensors into polymeric backbones via covalent link can be easily employed to fabricate devices and chips fixed onto microbioreactors, capable of avoiding the phase separation and concentration quenching of chromophores. With hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA, the main matrix of contact lens), a novel hydrophilic fluorescent copolymer P(NDI–HEMA) containing the pendant group of naphthalenediimide moiety (NDI) as low-cost pH chemosensor film for high-throughput microbioreactor was designed. Its film exhibits great sensitivity and stability when measured in aqueous solution, possessing an obvious fluorescent response with an excellent linearity in the pH range of 4.6–8.0 with an apparent pK_a of 6.0 corresponding to the methyl substituted piperidine nitrogen (N1) in NDI. The pH range is especially desirable to the fermentation monitoring of most industrially important microorganisms, such as various prokaryotes and eukaryotes. Furthermore, the long excitation wavelength at the isosbestic point of 572 nm and the emission band at about 630 nm of chromophore NDI brings several advantages such as low scattering, deep penetration, and minimal interfering absorption and fluorescence from biological system, showing a high promising application in bioprocess monitoring with a broad linear response range.