A simple, green method is described for the synthesis of Gold (Au) and Silver (Ag) nanoparticles (NPs) from the stem extract of Breynia rhamnoides. Unlike other biological methods for NP synthesis, the uniqueness of our method lies in its fast synthesis rates (~7 min for AuNPs) and the ability to tune the nanoparticle size (and subsequently their catalytic activity) via the extract concentration used in the experiment. The phenolic glycosides and reducing sugars present in the extract are largely responsible for the rapid reduction rates of Au(3+) ions to AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs (or AgNPs) and NaBH(4) was observed and was found to depend upon the nanoparticle size or the stem extract concentration used for synthesis.
The chemistry and interaction of thiones towards passivation, and self-assembly of metal nanoparticles is nascent and poorly understood. Here, we describe a sensitive (15 ppb) and rapid (<1 min) thiourea (TU) based self-assembly of citrate stabilized gold nanoparticles (AuNPs) into 1D arrays (or nanochains) through a non-crosslinking mechanism. The underlying principle for the nanochain formation is as follows: the displacement of negatively charged citrate with neutral TU in a Vromanlike effect introduces a surface polarity, which then drives the self-assembly of AuNPs into nanochains via the dipole-dipole interactions. Moreover, we find that the size of the nanochains can be controlled by regulating the strength of the resultant dipole, which depends on the physico-chemical parameters such as the zeta potential and hydrodynamic size. We further substantiate the dipole-based mechanistic pathway by demonstrating that addition of TU leads to a selective aggregation of electrostatically stabilized AuNP systems while sterically stabilized ones remain unaffected. The mechanism of ligand displacement (akin to Vroman effect) is supported by an increased sensitivity of the assembly process in the presence of NaHSO 4 . The soft-soft interactions of the gold-thione pair and the kinetics of ligand exchange were investigated and found to be influenced by the manner in which the substituents attached to the TU moiety modify the electron density around the thione sulphur. As demonstrated for TU detection (9.35 ppb) in sweet lime juice, the method serves as a simple, sensitive, selective, and rapid colorimetric assay for TU.
We sought to assess a smartphone-based, gold nanoparticle-based colorimetric lateral flow immunoassay paper sensor for quantifying urine 8-hydroxy-2 9 -deoxyguanosine (8-OHdG) as a biomarker for diabetic retinopathy (DR) screening.METHODS: Paper strips incorporate gold nanoparticle-8-OHdG antibody conjugates that produce color changes that are proportional to urine 8-OHdG and that are discernible on a smartphone camera photograph. Paper strip accuracy, precision, and stability studies were performed with 8-OHdG solutions of varying concentrations. Urine was collected from 97 patients with diabetes who were receiving DR screening examinations, including 7-field fundus photographs. DR was graded by standard methods as either low risk (no or mild DR) or high risk (moderate or severe DR). Paper sensor assays were performed on urine samples from patients and 8-OHdG values were correlated with DR grades. The differences in 8-OHdG values between the low-and highrisk groups were analyzed for outliers to identify the threshold 8-OHdG value that would minimize falsenegative results.RESULTS: Lateral flow immunoassay paper strips quantitatively measure 8-OHdG and were found to be accurate, precise, and stable. Average urine 8-OHdG concentrations in study patients were 22 ± 10 ng/mg of creatinine in the low-risk group and 55 ± 11 ng/mg of creatinine in the high-risk group. Screening cutoff values of 8-OHdG >50 ng/mg of creatinine or urine creatinine >1.5 mg minimized screen failures, with 91% sensitivity and 81% specificity.CONCLUSIONS: Urinary 8-OHdG is a useful biomarker to screen DR. Quantitative 8-OHdG detection with the lateral flow immunoassay paper sensor and smartphone camera demonstrates its potential in DR screening.
Dielectric analysis of nanometre range size ceramic particles like TiO 2 is very important in the understanding of the performance and design of their polymer nanocomposites for energy storage and other applications. In recent times, impedance spectroscopy is shown to be a very powerful tool to investigate the dielectric characteristics of not only sintered and/or pelleted ceramic materials but also particulates/powders (both micron-sized and nano-sized) using the slurry technique. In the present work, impedance spectroscopy employing slurry methodology was extended to study the influence of various chemical groups on the nano-TiO 2 surface on the electrical resistivity and the dielectric permittivity of nanoparticles. In this regard, different organophosphate ligands with linear, aromatic and extended aromatic nature of organic groups were employed to remediate the surface effects of nanoTiO 2. It was observed that the type of chemical nature of surface engineered nanoparticles' surface played significant role in controlling the surface electrical resistivity of nanoparticles. Surface passivated nanoTiO 2 yielded dielectric permittivity of about 70-80, respectively.
Current methods for capturing circulating tumor cells (CTCs) are based on the overexpression of cytokeratin (CK) or epithelial cell-adhesion molecule (EpCAM) on cancer cells. However, during the process of metastasis, tumor cells undergo epithelial-to-mesenchymal transition (EMT) that can lead to the loss of CK/EpCAM expression. Therefore, it is vital to develop a capturing technique independent of CK/EpCAM expression on the cancer cell. To develop this technique, it is important to identify common secondary oncogenic markers overexpressed on tumor cells before and after EMT. We analyzed the biomarker expression levels in tumor cells, before and after EMT, and found two common proteinshuman epidermal growth factor receptor 2 (Her2) and epidermal growth factor receptor (EGFR) whose levels remained unaffected. So, we synthesized immunomagnetic iron nanocubes covalently conjugated with antibodies of Her2 or EGFR to capture cancer cells irrespective of the EMT status. The nanocubes showed high specificity (6−9-fold) in isolating the cancer cells of interest from a mixture of cells spiked in serum. We characterized the captured cells for identifying their EMT status. Thus, we believe the results presented here would help in the development of novel strategies for capturing both primary and metastatic cancer cells from patients' blood to develop an effective treatment plan.
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