In this work, we describe an approach of detecting biomarkers by Surface Plasmon Resonance imaging (SPRi) technique in real samples. Two C-Reactive Protein (CRP)-antibody immobilization methods were used: The first method was based on direct physisorption of CRP-antibody onto gold surface; the second one was based on oriented CRP-antibody with protein G intermediate layer.The two developed immunosensors were tested against CRP antigen in phosphate buffer saline solution with the SPRi technique. The response of the developed immunosensors was reproducible and stable. The detection limit of 10 pg•mL −1 and 50 pg•mL −1 CRP-antigen was observed with and without protein G respectively with this technique. Moreover, the developed SPRi immunosensor was used for CRP-antigen detection in human plasma. A detection limit of 5 ng•mL −1 and 10 ng•mL −1 was obtained with and without protein G respectively. These obtained results were compared to those obtained with QCM (Quartz Crystal Microbalance) and Enzyme-Linked Immunosorbent Assay (ELISA) techniques.
Glycosylated albumin is considered as a potentially accurate indicator of shorter-term average glucose concentration compared with the current standard HbA1c and as such, it is attracting the interest of the scientific community as a possible diagnosis marker for diabetic patients. The purpose of this paper is to achieve a better understanding of the glycation effect of albumin on its electrochemical properties. That is done through the use of Interdigitated gold microelectrodes (IDGE) as support in a label free impedimetric immunosensor for the detection of human serum albumin detection in glycated (GA) and non-glycated (HSA) form. Anti-human serum albumin, a monoclonal antibody, was physisorbed on the surface of IDGE and used as a HSA/GA bioreceptor. Electrochemical impedance spectroscopy, cyclic voltammetry, and surface plasmon resonance imaging (SPRi) were used for the characterization of the grafted layers onto the gold surface. A detection range from 1 to 401 ng/mL of non glycated HSA antigen in phosphate buffered saline buffer was obtained with the impedance spectroscopy technique. The experiment led to the observation of a significant impedance difference between the glycated and non-glycated antigen of HSA. SPRi measurements confirmed these findings and allowed us to suggest an increase of the dielectric permittivity for human serum albumin upon glycation.
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