Abstract
Differential sensing techniques are becoming nowadays an attractive alternative to classical selective recognition methods due to the “fingerprinting” possibility allowing identifying various analytes without the need to fabricate highly selective binding recognition sites. This work shows for the first time that surfactant-based ion-sensitive microspheres as optodes in the microscale can be designed as cross-sensitive materials; thus, they are perfect candidates as sensing elements for differential sensing. Four types of the newly developed chemosensory microspheres—anion- and cation-selective, sensitive toward amine- and hydroxyl moiety—exhibited a wide range of linear response (two to five orders of magnitude) in absorbance and/or fluorescence mode, great time stability (at least 2 months), as well as good fabrication repeatability. The array of four types of chemosensitive microspheres was capable of perfect pattern-based identification of eight neurotransmitters: dopamine, epinephrine, norepinephrine, γ-aminobutyric acid (GABA), acetylcholine, histamine, taurine, and phenylethylamine. Moreover, it allowed the quantification of neurotransmitters, also in mixtures. Its selectivity toward neurotransmitters was studied using α- and β-amino acids (Ala, Asp, Pro, Tyr, taurine) in simulated blood plasma solution. It was revealed that the chemosensory optode set could recognize subtle differences in the chemical structure based on the differential interaction of microspheres with various moieties present in the molecule. The presented method is simple, versatile, and convenient, and it could be adopted to various quantitative and qualitative analytical tasks due to the simple adjusting of microspheres components and measurement conditions.
Highlights
The basis of any optical sensor is a molecule that changes optical properties in response to the presence of the analyte of interest [1]
Cation-selective microsphere suspensions were produced—this kind of optode is based on potassium tetraphenylborate salt as an ion exchanger, facilitating the exchange of cations between the aqueous and organic phase, which should lead to the deprotonation of chromoionophore, which is reported by change of its optical properties
This a very protonation beneficial effect bethus, an modes—spectrophotometric increase in lipophilic anions and concentration leads to is a higher degree cause they can be used as dual detection optodes, which allows increasing the accuracy of chromoionophore
Summary
The basis of any optical sensor is a molecule that changes optical properties in response to the presence of the analyte of interest [1]. The analyte activity can be detected indirectly by monitoring the hydrogen ion level in the sensor, which is reported by the change of optical properties of the chromoionophore. Such an indirect approach is very advantageous and versatile, since there is no need to synthetize the molecule having both a recognition part and reporter part covalently attached. By the careful designing composition of the cocktail, such nano/micro-optical sensors of differentiated selectivity can be developed Such miniaturized sensors usually have much shorter response times and smaller required sample volume, which are an advantage of optical micro/nanospheres over ISEs and bulk optodes [5,6,8]. The fluorimetric and spectrophotometric responses of optode microspheres obtained in the presence of neurotransmitters were examined to show the great potential of optode microspheres for differential sensing
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