Abstract
Developing a controlled method for obtaining hybrid enzymatic-based interfaces for sensing application require the use of a multiuse, reusable sensor. By controlling the interface characteristics in terms of the surface chemistry, thickness, and roughness, a tailored response toward various toxic compounds can be obtained, regarding both materials used as active surfaces and fabrication methods. Herein, we report a preliminary study on using a laser-based method (i.e., matrix-assisted pulsed laser evaporation, or MAPLE) for obtaining active polymeric–enzymatic interfaces as hybrid or layered coatings for detecting toxic vapors. The MAPLE fabrication consisted of the simultaneous alternating evaporation of layers of polyethylenimine (PEI) and acetylcholinesterase (AchE) in order to obtain active surfaces as both hybrid PEI-AchE and a PEI/AchE layered coating, respectively. The deposition processes of the polymer and enzyme were carried out using a double-target system and a Nd:YAG pulsed laser, operating at 0.45 J/cm2 fluences with a wavelength of 266 nm and a repetition rate of 10 Hz. Fourier transform infrared spectroscopy revealed no significant changes in the functional groups of both hybrid and layered coatings compared with the initial material. The thickness and roughness, as well as the morphologies of the coatings revealed by atomic force microscopy and scanning electron microscopy showed coatings thicker than two μm that had smooth surfaces and average roughness values below six nm. The sensors were tested with simulants for nerve gases and pesticides containing phosphonate ester groups, namely dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP), and a different sensitivity was shown to the selected chemical agents for each of the sensors. The best sensitivities for DMMP and DIMP obtained by using a PEI-AchE coated sensor are 65 kHz and 200 kHz, respectively, whereas the best sensitivity when using multilayered interfaces is 30 kHz and 10 KHz for DIMP and DMMP, respectively.
Highlights
Nowadays, the fast, sensitive detection of specific harmful chemical agents presents interest as a research topic, which is caused by security concerns and safety hazards
Examples of the SEM and atomic force microscopy (AFM) images of the samples obtained by both drop cast and matrix-assisted pulsed laser evaporation (MAPLE) are presented in Figure 2, and in Figures 3–5 for the samples obtained by MAPLE
This study demonstrated the feasibility of obtaining hybrid polymer–enzyme active interfaces for PEI-AchE sensors by using MAPLE and a modular target system
Summary
The fast, sensitive detection of specific harmful chemical agents presents interest as a research topic, which is caused by security concerns and safety hazards. Among the most used sensors, surface acoustic wave (SAW) sensors are used at a larger scale for research related to the detection of volatile toxic compounds due to specific characteristics: high sensitivity, small size, low cost, very good response time, and ability to work in wireless mode. The SAW sensor sensitivity and selectivity are related both to sensor characteristics and active area interface properties. This implies the use of specific compounds and methods that are compatible with them, which allow tailoring their characteristics [1,2,3,4,5,6,7].
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