This study reports on application of conductive silver paste smeared glass slides as Raman spectroscopy sample substrates for label-free detection of HIV-1 p24 antigen in blood plasma. It showed that the same substrates can be applied in Raman spectroscopic screening of blood plasma for presence of HIV. The characteristic Raman spectrum of HIV-1 p24 antigen displayed prominent bands that were assigned to Ribonucleic acids (RNA) and proteins that constitute the antigen. These spectra can be used as reference during Raman spectroscopic screening for HIV in plasma within the first few days after exposure (<7 days). The Raman spectra obtained from HIV+ plasma displayed unique peaks centered at wavenumbers 1270 and1446 cm-1 attributed to the Raman active vibrations in the virion proteins. Other bands similar to those reported in literature were also seen and assigned to lipids and carbohydrates. The attachment of the HIV virions to silver nanoparticles via gp120 glycoprotein knobs were thought to be responsible for the enhanced Raman signals of proteins associated with the virus. The principal component analysis (PCA) applied on the combined spectral data showed that HIV- and HIV+ spectra had differing spectral patterns. This indicated the great power of Raman spectroscopy in HIV detection when plasma samples are deposited onto silver paste smeared glass substrates. The Raman peaks responsible for the segregation of the spectral data in PCA were mainly those assigned to the viral proteins. Excellent results were also obtained from Artificial Neural Network (ANN) applied on the HIV+ data with R (coefficient of correlation) and R2 (coefficient of determination) values of 0.9958 and 0.9895, respectively. The method has the potential of being used as quick blood screening for HIV before blood transfusion with the Raman peaks assigned to the virion proteins acting as a reference.
Key words: Raman spectroscopy, HIV-1 p24 antigen, HIV+ and HIV-, PCA and ANN
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