We present a surface-enhanced Raman probe (SERS) platform for the determination of a prohibited substance, recombinant erythropoietin (rEPO), in urine matrix, using nanoparticles as substrate. Rod-shaped gold nanoparticles (GNR) were modified with a Raman label and an antibody as SERS probe. We developed two SERS-based immunoassays for detection and quantification of rEPO in urine. In the first assay, rEPO was determined by a sandwich assay with gold surfaces and GNR. In the second assay, rEPO was extracted by using core shell-structured magnetic iron oxide gold nanoparticles, and again sandwich assay was performed by using GNR. We also demonstrated the ability of the proposed method to discriminate rEPO and urinary erythropoietin (uEPO). A good linear correlation was obtained between logarithms of rEPO concentrations in urine and Raman intensities within the range of 10-10 pg mL rEPO concentrations. Detection limits which are smaller than 0.1 pg mL levels were achieved owing to the high extractive performance of the nanoextraction techniques. Graphical Abstract Schematic represantation of surface-enhanced Raman probe for rapid nanoextraction and detection of erythropoietin.
In this study, surface-enhanced Raman spectroscopy (SERS) based quantification method for the total protein using o-phthalaldehyde is reported for the first time. For this purpose, o-phthalaldehyde was chosen to form a complex with protein, and SERS signal was observed in the presence of gold nanoparticles. A calibration curve was obtained by plotting the intensity of the SERS signal at 727 cm À1 versus the concentration of protein standard (bovine serum albumin, BSA). Thus, the correlation was found to be linear within the range of 0.054-0.72 mg/ml of BSA, and the limit of detection was determined to be 0.08 mg/ml. All tests were carried out using a portable Raman instrument with an analysis time of 5 min. In addition, the ability of the developed method to quantify total protein in milk samples was investigated, and the obtained results were compared to the conventional ultraviolet methods.
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