Abstract
Saliva contains important personal physiological information that is related to some diseases, and it is a valuable source of biochemical information that can be collected rapidly, frequently, and without stress. In this article, we reported a new and simple localized surface plasmon resonance (LSPR) substrate composed of polyaniline (PANI)-gold hybrid nanostructures as an optical sensor for monitoring the pH of saliva samples. The overall appearance and topography of the substrates, the composition, and the wettability of the LSPR surfaces were characterized by optical and scanning electron microscope (SEM) images, infrared spectra, and contact angles measurement, respectively. The PANI-gold hybrid substrate readily responded to the pH. The response time was very short, which was 3.5 s when the pH switched from 2 to 7, and 4.5 s from 7 to 2. The changes of visible-near-infrared (NIR) spectra of this sensor upon varying pH in solution showed that—for the absorption at given wavelengths of 665 nm and 785 nm—the sensitivities were 0.0299 a.u./pH (a.u. = arbitrary unit) with a linear range of pH = 5–8 and 0.0234 a.u./pH with linear range of pH = 2–8, respectively. By using this new sensor, the pH of a real saliva sample was monitored and was consistent with the parallel measurements with a standard laboratory method. The results suggest that this novel LSPR sensor shows great potential in the field of mobile healthcare and home medical devices, and could also be modified by different sensitive materials to detect various molecules or ions in the future.
Highlights
Human body fluids such as saliva represent a typical medium, containing important personal physiological information that is related with some diseases [1,2,3,4,5,6,7,8]
Spherical and irregular-shaped nanostructures can be observed in the scanning electron microscope (SEM) image, along with gold nanoplates (GNPs) with edge length around 90–100 nm, and were randomly distributed on the glass substrate with a very low possibility of interparticle coupling due to the relatively large distance between different particles (Figure 1B)
The observable core/shell nanostructures in the SEM image of PANI-GNPs-glass indicated that the GNPs-glass substrates were successfully covered by a layer of polymer (PANI) (Figure 1C)
Summary
Human body fluids such as saliva represent a typical medium, containing important personal physiological information that is related with some diseases [1,2,3,4,5,6,7,8]. Compared to sweat and urine, saliva is more readily available—especially for those patients suffering from conditions that inhibit sweat production or who are suffering from chronic renal failure These advantages are especially important in the field of mobile healthcare and home medical devices. The sensor is composed of noble metal (e.g., gold) nanostructures, and shows an LSPR peak within the UV-vis-NIR region, and is highly sensitive to the refractive index of the environment near sensor surface. It is more sensitive and reliable than disposable pH test paper, which is based on color changes. The pH of a real saliva sample was monitored using this sensor, and the results were consistent with the parallel measurements taken with a standard laboratory method
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