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In this project, a sensitive fluorescent aptasensor was fabricated to detect lead ions (Pb 2+ ) by applying hollow gold nanoparticles (HGNPs) as a nano-carrier and rhodamine B (RDB) fluorescent dye as the signal agent. In the aptasensor that was created, the specific attachment of the aptamers to Pb 2+ ions led to the release of aptamer from the chitosan (CTS) coated-HGNPs loaded with RDB, causing an increase in fluorescence intensity due to the leakage of RDB. The method demonstrated specific detection of the target analyte, achieving a detection limit (LOD) of 1 ppb and a broad linear dynamic range spanning from 2 to 1000 ppb. The aptasensor was able to accurately measure the concentration of Pb 2+ in human serum, low-fat milk, and mineral water samples. The suggested biosensor, which offers the benefits of simplicity, user-friendliness, affordability, and high sensitivity, is well-suited for use with complex samples such as environmental and clinical samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Catalytic hairpin assembly (CHA)-DNA walker allows nanostructures to spontaneously hybridize to the nucleic acids. The localized surface plasmon resonance provides the ability of color-shift for Au nanoparticles (AuNPs) to design a colorimetric biosensor by implementing CHA-DNA walker reaction on AuNPs. A target gene in Klebsiella pneumoniae as the reaction cascade trigger, was selected. H1 and H2 oligonucleotides as the components of the system were designed and verified by NUPACK. The AuNPs were conjugated to H1. The conjugation of the probes to the AuNPs was evaluated using FT-IR. The signal amplification process was conducted at 25℃. TEM imaging, zeta potential, spectroscopy, and gel-electrophoresis were used to examine the conduction of the reaction cascade and specificity. The sensitivity of the method was analyzed using serial dilution of the target. The formation of over-52 bp intermediate secondary structures (which only exist when the reaction happens) was confirmed by gel-electrophoresis. The color distinction between positive (0.08 to 0.058) and negative samples (0.098 to 0.05) was evidenced instantly and in a period of 90 min of the reaction as a drop change of 520 nm intensity absorbance. TEM imaging confirmed the further distance of AuNPs in the positive sample in comparison to that of the negative sample which reveals effective detection of the pathogen. The LOD of the technique was measured as 2.5 nM of the target sequence. The diagnostic approach is a label-free, enzyme-independent approach and can be executed in a single step. It has been designed by employing the CHA-DNA walker system along with the colorimetric properties of AuNPs for the first time, thereby paving the way for more rapid and accurate diagnostic kits., (© 2024. The Author(s).)

Early detection of cancer increases the chance of effective treatment and survival rates. The aim of this study is to develop a rapid and non-invasive nano-biosensing method to screen common lethal cancers in their early stages. In that regard, two circulating microRNA (miR-21, miR-155) biomarkers, which are upregulated in plasma in prevalent cancers, were targeted by a rapid and colorimetric nano-biosensor based on non-crosslinking Au-nanoprobes without amplification requirement. Multiple cancerous cell lines, including A549, MCF7, HT-29, A2780, AGS, MKN-45, and SW-1736 and the primary fibroblast were examined with naked eyes after the hybridization assay using exogenous biomarkers. The results were also confirmed by spectroscopy analysis. The upregulated miRNAs in cancerous cell lines caused a significant blue shift in the Au-nanoprobe absorbance spectrum while the samples isolated from normal cells remained intact red. The limit of detection (LOD) of the method was determined to be less than one ng/µL of total isolated miRNA using an instrument-free visual method. The developed geno-sensing method could serve as a simple, point-of-care platform for cancer prognosis and diagnosis, leading to operative nano-theranostics., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The extracted miR-21 and miR-155 from the plasma of clinical samples were targeted by non-crosslinking hybridization of Au-nanoprobes without the need for biomarker amplification. Thirty samples, including those suspected to cancer and chemotherapy-treated samples, were analyzed. An increase in the concentration of target biomarkers caused a blue-shift in the visible spectrum of nanoprobes. Using magnesium chloride, the change in the color of nanoprobes was shown to be dependent on time besides intensity. Samples with high averages of intensity needed less time for colorimetric differentiation than those with low average intensity. Au-nanoprobe-21 was turned to purple-gray in clinical specimens of stomach, colon, breast, esophagus, sarcoma, diaphragm, prostate, bladder, and lung while Au-nanoprobe-155 appeared as light purple-gray in colon, breast, lung, diaphragm and esophagus samples. The LOD was measured as 5 ng μL -1 of targeted biomarkers. The developed nano-biosensing method could propose a point-of-care approach for cancer prognosis and diagnosis, facilitating targeted therapeutics., (Copyright © 2020 Elsevier Inc. All rights reserved.)