title: Conductive silver paste smeared glass substrates for label-free Raman spectroscopic detection of HIV-1 and HIV-1 p24 antigen in blood plasma.
abstract: 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-1attributed 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-1). Excellent results were obtained from Artificial Neural Network (ANN) applied on the HIV+ Raman spectral data around the prominent peak centered at 1270 cm-1with 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 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.
authors.affiliation: Department of Physics, Egerton University, P.O Box 536-20115, Egerton, 20115, Kenya.
authors.forename: Ben O
authors.initials: BO
authors.lastname: Otange
authors.affiliation: Department of Physics, University of Nairobi, P.O Box 30197-00100, Nairobi, 00100, Kenya. birech@uonbi.ac.ke.
authors.forename: Zephania
authors.initials: Z
authors.lastname: Birech
authors.affiliation: Department of Physics, University of Nairobi, P.O Box 30197-00100, Nairobi, 00100, Kenya.
authors.forename: Justus
authors.initials: J
authors.lastname: Okonda
authors.affiliation: Department of Physics, Egerton University, P.O Box 536-20115, Egerton, 20115, Kenya.
authors.forename: Ronald
authors.initials: R
authors.lastname: Rop
mesh_terms: D004867:Equipment Design; D005898:Glass / Q000737:chemistry; D016655:HIV Core Protein p24 / Q000097:blood*; D015658:HIV Infections / Q000097:blood*; D015497:HIV-1 / Q000302:isolation & purification*; D006801:Humans; D053768:Metal Nanoparticles / Q000737:chemistry; D025341:Principal Component Analysis; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000295:instrumentation / Q000379:methods*
chemical_list: D016655:HIV Core Protein p24; D012834:Silver
keywords: Artificial Neural Networks; HIV positive plasma; HIV-1 p24 antigen; Principal component analysis; Raman spectroscopy