Towards HIV detection: Novel poly(propylene imine) dendrimer-streptavidin platform for electrochemical DNA and gp120 aptamer biosensors

The detection of sequence - specific DNA and HIV glycoprotein 120 (gp120) based on novel generation 4 poly(propylene imine) dendrimer/streptavidin platform is reported. The platform was prepared by the electrodeposition of the dendrimer on a carbon electrode followed by drop coating with streptavidin. The generation 4 poly(propylene imine) dendrimer/streptavidin platform was characterised using scanning electron microscopy, voltammetry and electrochemical impedance spectroscopy (EIS). Electrochemical measurements indicated that the platform was stable, conducting and exhibited reversible electrochemistry at a former potential of 140 mV in pH 7.5 phosphate buffer saline solution (PBS), while EIS interrogation using [Fe(CN)₆^3-/4-] redox probe showed a marked reduction in charge transfer resistance (R_ct) after modification. The biosensor was prepared by the immobilisation of single stranded 5'- biotynilated probe DNA and B40 aptamer on the modified electrode and then used to detect complementary DNA and gp120 respectively. The biosensor responses were evaluated with square wave voltammetry (SWV) and EIS in the presence of PBS and Fe(CN)63-/4- redox probe. A detection limit of 3.44 x 10^-12 M (S/N = 3) and linearity r² = 0.9985 were obtained for the DNA biosensor while the aptamer biosensor detected gp120 in the nanomolar concentration range. The DNA biosensor also showed excellent selectivity in the presence of non complementary and mismatch DNA strands.