- Ion-selective polymeric optical sensors – ion optodes – are a promising alternative to ion-selective electrodes and fluorescent dyes for analytical and biological applications, e.g. extra- and intracellular measurements. They are non-toxic, highly selective robust probes for ionic fluxes monitoring.
A large-scale fabrication of ion optodes using a solvent displacement method is introduced. This method is a single-batch process that does not require any additional steps. The influence of numerous parameters, e.g. surfactant concentration, solvent nature and membrane concentration, on the average size of the synthesized optodes was studied. The solvent displacement method allows control of the particle size in 200 nm to 30 μm range.
Ion optodes selective for sodium, potassium, and calcium cations were prepared and calibrated for hydrogen (pH), sodium, potassium, and calcium. Fabricated
sensors demonstrated excellent selectivity, low drift, high stability and reproducibility.
Further studies of ion-optodes of different sizes but the same chemical composition revealed a significant shift in their response function. This bias is clearly seen for all fabricated optodes. A strong correlation between a calculated specific surface area and the apparent ion-exchange constant was observed. Considering this, it may be hypothesized that the surface phenomena are contributing to the overall optode response resulting in the observed effect. As a consequence, the response models, developed for the macroscopic ion optodes, cannot be easily applied to the probes at micron- and nano-scale.
A primary concern for continuous sensing application of optical sensors is photobleaching of lipophilic fluorescent dye which prevents quantitative fluorescence measurements. Quantum dots, known for their high photostability, brightness and broad excitation spectra with narrow emission bands, were incorporated into polymeric matrix. They excited a fluorophore indirectly, thus, reducing its photobleaching and increasing sensors life-time. We created a composite, quantum dots doped, polymeric sensor that can be integrated into high-throughput detection platforms, such as flow cytometry, chip-based micro-total analysis system technologies, or bundled optical fiber arrays.
Ultimately, a fabricated ion-optode was introduced into a Boolean logic gate serving as a reporting microparticle. It responded to the pH changes generated in situ by the enzyme logic system. The present work aimed scaling down the size of biocomputing functional units which might reach the information processing by single molecules associated with signal-transducing single nanoparticles.