Bisphenol A (BPA) is used in a wide variety of consumer products owing to its beneficial properties of optical clarity, shatter resistance, and heat resistance. However, leached BPA has been shown to disturb the endocrine system and could cause cancer even at low concentrations, which has led to public concern. To reduce the toxic effects caused by BPA, it is important to monitor the BPA levels and its presence in products in a simple, rapid, and on-site manner. Here, we propose a new colorimetric strategy for the simple and rapid detection of BPA employing a DNA aptamer, a cationic surfactant, and gold nanoparticles (AuNPs). Using the developed system, the presence of BPA can be successfully determined based simply on a visually detectable color change from red to blue, triggered by aggregate formation of the AuNPs, which can be monitored even with the naked eye. Under the optimized conditions, this system could detect BPA with excellent selectivity and sensitivity, and its high performance was validated in the receipt obtained from local market and BPA-spiked tap water samples, ensuring its practical applicability. Moreover, the limit of the detection of the system was determined to be 97 nM, which is below the current tolerable daily intake level, demonstrating its suitability for toxicity assessment and on-site quality control in a more economical manner when compared with conventional methods.

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A new method has been developed for the simple, fluorescence, turn-on detection of melamine, which utilizes DNA-templated silver nanoclusters (DNA-AgNCs) as a key component. In the sensor, melamine exhibits the dual functions: one is to enhance the fluorescence signal of DNA-AgNCs by its specific interaction with thymine residues in DNA template, and the other is to prevent Hg(II)-induced fluorescence quenching of DNA-AgNCs via its strong coordination with Hg(II). These consequently enable the sensitive and selective detection of melamine. By exploiting such novel features of melamine, we significantly increased the fluorescence response up to 360%, compared to the previous counterpart that relies on DNA-AgNCs only, and successfully determined melamine down to ca. 49 nM, a value that is 400 times lower than the safety level of 20 lM set by the US Food and Drug Administration. In addition, it was confirmed that the proposed approach works fine even in the real milk samples without any additional pre-treatment steps.

Siddha medicine was developed by ancient Tamil sages known as 'Siddhars' and has been in use for more than 5,000 years [1]. It involves the use of gold, zinc and silver formulated with honey, ghee, or milk to cure diseases [2,3]. Prototypical examples include Swarna Bhasma (gold ash), Jasada Bhasma (zinc ash), and Rajath Bhasma (silver ash), which are prepared by processing a fine powder of gold, zinc, and silver with plant extract, followed by repeated incineration at high temperature (~1,000°C). During incineration, the size of the fine powder of gold, zinc, and silver is reduced to that of chemically synthesized nanoparticles (1-100 nm). This fine powder is composed of individual particles of around 50-70 nm in size; however, these particles are prone to forming large aggregates, unlike chemically synthesized nanoparticles [4].Compared with gold-derived Swarna Bhasma and zinc-derived Jasada Bhasma, the silver-derived medicine Rajath Bhasma has superior and broad-spectrum antimicrobial, antifungal, and antiviral activities [5] and hence numerous applications. Notably, Rajath Bhasma has been used to treat various disorders including anxiety, aging, and infertility [6][7][8]. The physical characteristics of a silver preparation are believed to markedly influence its therapeutic properties; however, despite its widespread use in India, the exact chemical composition/structure of Rajath Bhasma and its biological activities are largely unknown. Current tools for characterizing these particles at the nanoscale level have furthered the understanding of the parameters directly or indirectly influencing the efficacy of these ancestral medicines. Accordingly, efforts have been made to study these particles at the nanoscale level. For example, Mitra et al. [9] have characterized Swarna Bhasma (gold ash) and Jasada Bhasma (zinc ash) and Rohit et al. [10] reported the synthesis of Rajath Bhasma through a simple characterization method.In general, Rajath Bhasma is safe for therapeutic applications [9]; however, in vivo studies are required to accurately predict its toxicity. Zebrafish embryos are a well-established in vivo model for evaluating teratogenicity.In India, nanotechnology has been used in therapeutic applications for several millennia. One example of a traditional nanomedicine is Rajath Bhasma (also called calcined silver ash), which is used as an antimicrobial and for the treatment of various ailments and conditions such as memory loss, eye diseases, and dehydration. In this study, we aimed to characterize the physical composition and morphology of Rajath Bhasma and its suitability for use as a non-toxic antimicrobial agent. First, Rajath Bhasma was physically characterized via i) Fourier-transform infrared spectroscopy to analyze the surface functional groups, ii) scanning electron microscopy coupled with energydispersive X-ray spectroscopy to observe the morphology and elemental composition, and iii) X-ray diffraction to determine the crystalline phases. Thereafter, functional characterization was performed thr...