Low level: The amount of arsenic in Bangladeshi well water and in bottled drinking water and Mississippi tap water are indicated by a dynamic light scattering (DLS) assay. Label‐free gold nanoparticles are used in a selective colorimetric assay (see picture) and in a highly sensitive DLS assay for the recognition of arsenic in concentrations as low as 3 ppt.

The presence of E coli in foodstuffs and drinking water is a chronic worldwide problem. The worldwide food production industry is worth about U.S. $578 billion, and the demand for biosensors to detect pathogens and pollutants in foodstuffs is growing day by day. Driven by the need, we report for the first time that two-photon Rayleigh scattering (TPRS) properties of gold nanorods can be used for rapid, highly sensitive and selective detection of Escherichia coli bacteria from aqueous solution, without any amplification or enrichment in 50 Colony Forming Units (cfu)/mL level with excellent discrimination against any other bacteria. TPRS intensity increases 40 times, when anti E. coli antibody-conjugated nanorods were mixed with various concentrations of Escherichia coli O157:H7 bacterium. The mechanism of TPRS intensity change has been discussed. This bionanotechnology assay could be adapted in studies using antibodies specific for various bacterial pathogens for the detection of a wide variety of bacterial pathogens used as bioterrorism agents in food, clinical samples, and environmental samples.

Alzheimer’s disease (AD) is a progressive mental disorder disease, which affects 26.6 million people in worldwide and estimated increments can be 100 millions by 2050. Since there is no cure at present, early diagnosis of AD is crucial for the current drugs treatments. Driven by the need, here we demonstrate for the first time that monoclonal ani-tau antibody coated gold nanoparticle based two-photon scattering assay can be used for the detection of Alzheimer’s tau protein in 1 pg/mL level which is about two orders of magnitude lower than cut-off values (195 pg/mL) for tau protein in CSF (cerebrospinal fluid). We have shown that when ani-tau antibody coated gold nanoparticle were mixed with 20 ng/ml of tau protein, two-photon Rayleigh scattering intensity (TPRS) increases by about 16 times. The mechanism of TPRS intensity change has been discussed. Our data demonstrated that our TPRS assay is highly sensitive to Tau protein and it can distinguish from BSA, which is one of the most abundant protein components in CSF. Our results demonstrate the potential for a broad application of this type of nano-bionanotechnology in practical biomedical applications.

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Ganz wenig genügt: Der Gehalt von Arsen in Brunnenwasser in Bangladesh sowie in käuflichem Trinkwasser und in Leitungswasser im US‐Staat Mississippi kann mithilfe eines Assays auf der Basis dynamischer Lichtstreuung (DLS) angezeigt werden. Die hochempfindliche und selektive colorimetrische Analyse (siehe Bild) weist Arsen in Konzentrationen von nur 3 ppt nach.