Sub-attomolar electrochemical measurement of DNA hybridization based on the detection of high coverage biobarcode latex labels at PNA-modified screen printed electrodes

We have constructed biobarcode labels based on 468 nm diameter latex spheres. Modification with polyallylamine and then glutaraldehyde was used to attach a high DNA loading, consisting of aminated probe DNA (approx. 1.01×10² molecules per sphere) and biobarcode DNA (approx. 1.66×10⁴ molecules per sphere). Detection of the biobarcodes was performed by application of a Ag enhancer solution, causing association of the Ag⁺ ions with the phosphate groups of the DNA. The deposited Ag was detected by differential pulse voltammetry. A 30 mer sequence from the BL21 strain of E. coli was detected with an LOD of 2.6 fM (calibration range 10 aM to 0.1 pM, r²=0.91, n=45). The LOD was lowered to 0.56 aM (calibration range 100 zM to 0.1 nM, r²=0.991, n=50) by utilizing a sandwich assay with PNA-modified screen printed electrodes, which lowered the Ag background current. The sandwich assay platform was used to calibrate E. coli strain BL2(DE3) with an LOD of 17.0 CFU mL⁻¹ (calibration range 10 to 10⁶ CFU mL⁻¹, r²=0.99, n=33) with good discrimination against Salmonella.