Unconventional Application of Conventional Enzymatic Substrate: First Fluorogenic Immunoassay Based on Enzymatic Formation of Quantum Dots

In this study, a simple fluorogenic immunoassay based on in situ formation of semiconductor quantum dots (QDs) is described. We discovered that alkaline phosphatase (ALP), the enzyme broadly used in enzyme-linked immuno-sorbent assay (ELISA), is able to trigger formation of fluorescent CdS QDs. ALP-catalyzed hydrolysis of <i>p</i>-nitrophenyl phosphate (pNPP) leads to the formation of <i>p</i>-nitrophenol and inorganic phosphate. The latter stabilizes CdS QDs produced in situ through interaction of Cd²⁺ with S^2– ions. So, the specific interaction of analyte (antibody) with ALP-labeled antibody can be detected through formation of CdS QDs, monitored by recording emission spectra at λ_ex = 290 nm. The fluorescence intensity showed to be dependent on the concentration of target antibody. This method allowed us to detect as low as 0.4 ng mL^–1 of analyte antibody with a linear range up to 10 ng mL^–1. The sensitivity of this novel assay showed to be 1 order of magnitude better than that of the standard method based on colorimetric <i>p</i>-nitrophenyl phosphate assay

Detection of Influenza Virus Using Peroxidase-mimic of Gold Nanoparticles

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High sensitivity, high selectivity SERS detection of MnSOD using optical nanoantennas functionalized with aptamers

International audienceIn this paper, we present the development of a highly sensitive, specific and reproducible nanobiosensor to detect one specific liver cancer biomarker, the manganese super oxide dismutase (MnSOD). The high sensitivity and reproducibility was reached by using SERS on gold nanostructures (nanocylinders and coupled nanorods) produced by electron-beam lithography (EBL). The specificity of the detection was provided by the use of a specific aptamer with high affinity to the targeted protein as a recognition element. With such a sensor, we have been able to observe the SERS signal of the MnSOD at concentrations down to the nM level and to show with negative control that this detection is specific due to the use of the aptamer. This latter issue has allowed us to detect the MnSOD in different body fluids (serum and saliva) at concentrations in the nM range. We have then demonstrated the effectiveness of our SERS nanobiosensor using aptamer as a bioreceptor for the detection of disease biomarker at low concentration and in complex fluids