Abstract
The characterization of nanostructured thin films is critical in the design and fabrication of optical sensors. Particularly, this work is a detailed study of the properties of layer-by-layer electrostatic self-assembled multilayer (LbL) structures fabricated using poly(allylamine hydrochloride) (PAH) and Neutral Red (NR) as cations, and poly(acrylic acid) (PAA) as polyanion. These LbL films, due to the colorimetric properties of the NR, are suitable for sensor applications such as pH sensing in the physiological range. In the (PAH+NR/PAA) LbL structure, it has been observed a very important influence of the pH of the solutions in the properties of the resultant films. Different techniques such as spectroscopy and atomic force microscopy (AFM) are combined to characterize the films, and the results are analyzed showing coherence with previous works. The LbL structure is finally optimized and dramatically improved nanostructured films were fabricated, showing good sensing properties, short response times, and good stability.
Highlights
Optical sensing is becoming a real alternative to the conventional sensors in some applications because of their important advantages as electromagnetic immunity, biocompatibility, multiplexing, miniaturizing capability, and so forth
The self-assembly of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) processes is altered by the addition of the neutral red (NR) to the polycationic solution
The thickness results of the (PAH + NR/PAA)n structure were studied to characterize the films, and the previous work with (PAH/PAA)n reported by Shiratori and Rubner [23] was taken as reference in the following analysis
Summary
Optical sensing is becoming a real alternative to the conventional sensors in some applications because of their important advantages as electromagnetic immunity, biocompatibility, multiplexing, miniaturizing capability, and so forth. The LbL technique, first reported by Decher [6], is a very versatile tool useful in creating multilayer structures in the nanometric range With this technique it is possible to tune the composition of the layers at molecular scale, fabricate interesting composite materials in a simple and inexpensive way onto substrates composed by almost any material and with almost any size or shape. This technique has been successfully demonstrated in many applications such as conductive coatings [7], antireflective coatings [8], sensitive coatings [9,10,11,12,13,14], organic light emitting diodes [15], photovoltaic cells [16], and so forth
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