We report 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. We also show 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. This spectrum 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 928, 990, 1270, 1397, and 1446 cm attributed to the Raman active vibrations in the virion carbohydrates, lipids, and proteins. Other bands similar to those reported in literature were also seen and assignments made. The attachment of the HIV virions to silver nanoparticles via gp120 glycoprotein knobs was 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 (645, 725, 813, 1270, and 1658 cm). Excellent results were obtained from Artificial Neural Network (ANN) applied on the HIV+ Raman spectral data around the prominent peak centered at 1270 cm with R (coefficient of correlation) and R (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 reference. Graphical Abstract The HIV type 1 virus particle gets attached to the silver nanoparticle contained in the conductive silver paste smear onto a glass slide. This results in strong Raman signals associated with the components of the virion. The signals are collected, dispersed in a spectrometer and displayed on a computer screen. Method can be used as a label-free and rapid HIV screening in blood plasma.
Most HIV viral load determination techniques available commercially are anchored on direct measurements of either HIV ribonucleic acid (RNA), provirus DNA, or viral antigen. Such techniques often require expensive reagents which makes the process expensive. This study reported the feasibility of label‐free determination of HIV‐1 viral load in plasma based on the consequence of the virus in the components of plasma. The study aimed to provide a relatively cheap and faster HIV‐1 detection and further estimate the concentration of the virus without using any reagent. We subjected 22 HIV‐1‐infected human plasma samples to Raman peak height evaluation to develop a detection and concentration estimation model for HIV‐1. Simultaneously, all the samples were examined for HIV‐1 infection using qualitative polymerase chain reaction (PCR) test. The positive samples were further subjected to quantitative PCR to determine their corresponding viral load. Principal component analysis (PCA) and artificial neural network (ANN) were employed in Raman spectral analysis to enhance label‐free detection of the HIV‐1 in plasma. The quantification model results for HIV‐1 yielded a good correlation with those obtained by the reference quantitative PCR method. HIV‐1 viral load estimation based on the associated Raman spectral peaks centered at 1,270 and 1,446 cm−1 achieved a clinically accepted coefficient of determination (R2 > 0.9). The viral detection sensitivity from the two associated peaks were 95 and 100 copies of the virus per milliliter of plasma, respectively, hence showing that the Raman‐based model can be a potential HIV‐1 diagnostic and viral load estimation tool.
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