Ionic liquid-based optoelectronic sensor arrays for chemical detection

Abstract

Development of ionic liquid (IL)-based colorimetric sensor arrays for detection and identification of chemicals in both the aqueous and vapor phases is reported. These facile and inexpensive optoelectronic sensors were fabricated by using ionic liquids (ILs) derived from readily available pH indicator dyes. A series of 12 different chemosensory ILs were synthesized by pairing anionic pH indicator dyes with trihexyl(tetradecyl)phosphonium ([P 66614 ]) cation via an ion exchange reaction. The incorporation of the [P 66614 ] cation imparted hydrophobic characteristics to these ILs, and this induced hydrophobicity led to their desired low solubility in aqueous solutions, as well as eliminated the need for a specialized hydrophobic matrix/substrate for immobilization. In this manuscript, four different matrices, i.e. glass microfiber filter papers, cotton threads, silica thin layer chromatography (TLC) plates, and alumina TLC plates, were employed for fabrication of sensor arrays. These sensor arrays were used to analyze pH values of aqueous solutions as well as for detection of acidic and basic vapors. To further prove the applicability of these IL sensor arrays as tools to sense closely related complex materials, the arrays were applied to successful discrimination of aqueous solutions of smoke from three commercially available cigarettes. The digital data generated from these sensor arrays were used in developing predictive models for accurately identifying various analytes. Two approaches were used for developing the models, and two methods were applied for assessing the predictive accuracy of the models. Use of cotton threads as a matrix led to development of a more flexible, low volume, and lightweight array to estimate pH and detect a variety of vapors. These wearable arrays may possibly be incorporated into bandages, sweatbands, diapers, and similar systems. Overall, these IL-based sensor arrays should provide a new research direction in the development of advanced colorimetric sensor arrays for detection and identification of a range of analytes relevant to many different applications.

Applications of Ionic Liquids for the Development of Optical Chemical Sensors and Biosensors

“…The selectivity of the detection of acidic/ basic vapors using disposal photonic IL-coated materials depended on the nature of the used matrix (a cotton thread, a filter paper, silica or alumina TLC plate). 83 This finding seemed to be very useful for the chemical detection of a variety of vapors that had been demonstrated on the example of analysis of aqueous solutions of cigarette's smoke. 83 The wearable sensors in the form of cotton threads have a great potential for military applications.…”

“…83 Such sensing materials include silica and alumina TLC plates, filter paper, and cotton thread matrices ( The optical fibers coated by porous polyelectrolyte membranes (PPMs) is an example of the use of PILs in the IL-coated materials for pH monitoring (Fig. 1.5.D).…”

“…83,86 Then the scanned images are divided into color-uniform parts, which are processed using image analysis software, to calculate the mean values of the color components, R, G, B (red, green, blue) and H, S, V (hue, saturation, value) along with their dispersions. 83,86 The miniature devices based on microfluidic and centrifugal platforms with incorporated ionogels are worth a special mention. One kind of device, a wearable chemical barcode micro-fluid platform, allows monitoring of the pH of sweat in real-time by comparison of the observed color of an ionogel with a standard color chart or using photo and video analysis of the color changes.…”

“…83 The resultant pH sensitive IL-coated materials could work in aqueous solutions without leaching IL.…”

“…8). 57 Chromogenic agents (i.e., different acid-base indicators and HPTS) embedded into IL-coated materials 83 and [P6,6,6,14]3HPTS-based films 49 changed their optical characteristics in the presence of vapors of various acids and bases, including organic compounds (Fig. 9).…”