Micro- and Nanostructured Polyaniline for Instant Identification of Metal Ions in Solution.

Agnieszka Michalska,Jerzy Langer,Sebastian Golczak,Krzysztof Langer

doi:10.3390/nano9020231

Agnieszka Michalska, Jerzy Langer + Show 2 more

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https://doi.org/10.3390/nano9020231

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Abstract

The unique properties of nanomaterials enable the creation new analytical devices. Polyaniline (PANI) micro- and nanofiber network, freestanding in the gap between two gold microelectrodes, has been used in a new nanodetector for metal ions in solutions. The gold electrodes were modified with the aid of alkanethiols, forming a self-assembled monolayer (SAM), which is able to block the ion current flow, but also to interact with metal ions when specific functional molecules are incorporated into the layer. The electric field of the trapped metal ions induces change of the electrical conductivity of polyaniline nanofibers in vicinity. A small injected sample (75 μL) of a solution of salt (about 0.5 μg of salt) was enough to induce a reproducible change in the electrical conductivity of polyaniline nano-network, which was registered as a function of time within 10–20 s. The response was proportional to the concentration of ions. It also depends on properties of ions, e.g., the ionic radius, which allows for identification of metal ions by analyzing the parameters of the signal: the retention time (RT), half width (HW), amplitude (A) and integral intensity (INT). The advantage of the new device is the instant responsiveness and easy operation, but also the simple construction based on organic (polymer) technology. The system is “open”—when learned and calibrated adequately, other metal ions can be analyzed. The nanodetector can be used in cases where monitoring of the presence and concentration of metal ions is important.

Highlights

Advances in nanotechnology have led to the development of new types of efficient and inexpensive chemical and biological sensors and detectors
The main part of the nanodetector for the detection of metal ions in the solution was an active working layer with a thickness of 5–10 μm. It consisted of a network of polyaniline nanofibers with almost uniform fiber diameters of 0.2–0.5 μm (Figure 3B)
The best functionality and the best protection against the “parasitic” ion current were achieved with the aid of a monolayer, formed of mixed alkanethiols: pentanethiol (Pnt) and 3-[tris(2-methoxyethoxy)silyl]-propane-1-thiol (Si2t) at a molar ratio of 4:1, Pnt-Si2t (Figure 3A)

Summary

Introduction

Advances in nanotechnology have led to the development of new types of efficient and inexpensive chemical and biological sensors and detectors. Those new devices are being designed and fabricated as a new class of analytical equipment, operating in the nano- or/and micro-scale [1]. The active part of the device can be fabricated from silicon nanowires [10,11], carbon nanotubes [12,13] or polyaniline nanofibers [14,15,16,17]. Polyaniline is a conducting polymer with a uniquely simple doping mechanism, based on acid-base reactions. The change of resistance of nanofibril polyaniline is more than 10 times faster than that of conventional polyaniline thin film [18,19,20,21,22]

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