The detection of single nucleotide polymorphisms (SNPs)
is of increasing
importance in many areas including clinical diagnostics, patient stratification
for pharmacogenomics, and advanced forensic analysis. In the work
reported, we apply a semiautomated system for solid-phase electrochemical
melting curve analysis (éMCA) for the identification of the
allele present at a specific SNP site associated with an increased
risk of bone fracture and predisposition to osteoporosis. Asymmetric
isothermal recombinase polymerase amplification using ferrocene labeled
forward primers was employed to generate single stranded redox labeled
amplicons. In a first approach to demonstrate the proof of concept
of combining asymmetric RPA with solid-phase éMCA, a simplified
system housing a multielectrode array within a polymeric microsystem,
sandwiched between two aluminum plates of a heater device, was used.
Sample manipulation through the microfluidic channel was controlled
by a syringe pump, and an external Ag/AgCl reference electrode was
employed. Individual electrodes of the array were functionalized with
four different oligonucleotide probes, each probe equivalent in design
with the exception of the middle nucleotide. The isothermally generated
amplicons were allowed to hybridize to the surface-tethered probes
and subsequently subjected to a controlled temperature ramp, and the
melting of the duplex was monitored electrochemically. A clear difference
between the fully complementary and a single mismatch was observed.
Having demonstrated the proof-of-concept, a device for automated éMCA
with increased flexibility to house diverse electrode arrays with
internal quasi-gold reference electrodes, higher resolution, and
broader melting temperature range was developed and exploited for
the detection of SNP hetero/homozygosity. Using the optimized conditions,
the system was applied to the identification of the allele present
at an osteoporosis associated SNP site, rs2741856, in 10 real fingerprick/venous
blood samples, with results validated using Sanger sequencing.