Highly-sensitive detection of a K-ras point mutation in codon 12, frequently found in pancreatic cancer, based on DNA-carrying hydrogel microspheres as a response enhancer for surface plasmon resonance (SPR), is described. Acrylamide-based microspheres with carboxyl groups were conjugated with DNA probes. Use of the DNA-carrying microsphere in the sandwich method, that is, binding of the microspheres with target DNAs at the sensor surface, enhanced the SPR response as a combined result of increased dielectric constant by the DNA-carrying microspheres. Microspheres lead to response enhancement, as shown by a 100-fold increase in sensitivity compared to that of non-amplified DNA target hybridization. In addition, the advantage of peptide nucleic acid (PNA) in the detection of a K-ras point mutation at the sensor surface by increasing temperature and flow rate is discussed. Results illustrate that the sandwich method through DNA-carrying microspheres for a SPR sensor is a promising approach for ultrasensitive DNA detection.
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