RESUMO
Herein, we reported a wearable photodetector based on hybrid nanocomposites, such as carbon materials and biocompatible semiconductor nanocrystals (NCs), exhibiting excellent photoresponsivity and superior durability. Currently, semiconductor nanocrystal quantum dots (QDs) containing heavy metals, such as lead or cadmium (in the form of lead sulfide (PbS) and cadmium sulfide (CdS)), are known to display excellent detection properties and are thus widely employed in the fabrication of photodetectors. However, the toxic properties of these heavy metals are well known. Hence, in spite of their enormous potential, the QDs based on these heavy metals are not generally preferred in biological or biomedical applications. These limitations, though, can be overcome by the judicious choice of alternate materials such as silver sulfide (Ag2S) NCs, which are biocompatible and exhibit multiple excitons in Ag2S QDs. The other chosen component is a carbon-based material, such as the multi-walled carbon nanotube (MWCNT), which is preferred primarily due to its strong and superior mechanical durability. In this study, a hybrid nanocomposite film was synthesized from Ag2S NCs and MWCNTs by a simple one-step fabrication process using ultrasonic irradiation. Additionally, this method did not involve any chemical functionalization or post-processing step. The size of Ag2S NCs in the hybrid film was controlled by the irradiation time and the power of the ultrasonic radiation. Further, appropriate composition ratio of the hybrid composite was optimized to balance the photo-response and mechanical durability of the photodetector. Thus, using this synthetic method, an excellent photoresponsivity property of the device was demonstrated for a near-infrared (NIR) light source with various light wavelengths. Furthermore, no visible change in photoresponsivity was observed for bending motions up to 105 cycles and for a range of angles (0-60°). This novel method provides an eco-friendly alternative to existing functional composites containing toxic heavy metals and is a promising approach for the development of wearable optoelectronic devices.
RESUMO
The rabbit pyrogen test and Limulus amoebocyte lysate (LAL) assay have been used to detect endotoxins in vaccines, but interactions between the endotoxins and proteins or aluminum hydroxide can interfere with the results. Currently, the rabbit pyrogen test is used to detect endotoxin in hepatitis B (HB) vaccines even though the HB surface protein, the active ingredient, is over-expressed in and purified from eukaryotic cells which lack endotoxin. Therefore, we examined the possibility of replacing the animal tests with the more efficient LAL test. To this end, we determined whether the aluminum hydroxide in the HB vaccines affects the rabbit pyrogen test and the LAL assay. HB vaccines and HB protein solutions spiked with lipopolysaccharide (LPS) produced almost the same dose-dependent temperature rise in rabbits, indicating that the aluminum hydroxide in the HB vaccine does not interfere with the pyrogenic response in rabbit. In contrast, a spike recovery study showed that aluminum hydroxide interfered with the LAL clot and kinetic assays; however, the LAL clot assay was effective at detecting endotoxin without loss of LAL activity after serial dilution of the samples. Furthermore, there was good correlation in the LAL clot assay between the amount of LPS added and the amount recovered. However, both turbidimetric and chromogenic kinetic assays displayed no correlation between the LPS amount added and recovered. Our results suggest that the LAL clot assay is sensitive and reliable when samples are properly prepared, and can be used to replace the rabbit pyrogen test for the detection of endotoxin in HB vaccines.