Abstract
We report on a colorimetric lysozyme (LZ) assay that is based on the aggregation of gold nanoparticles (AuNPs) induced by poly(diallyldimethylammonium chloride) (PDDA) and an LZ-specific 25-base aptamer. The method is based on the finding that AuNPs undergo aggregation on addition of PDDA. If, however, aptamer is present, it will undergo electrostatic interaction with PDDA to form a duplex structure. Hence, the aggregation of AuNPs is suppressed. Upon the addition of LZ, the aptamer will bind to LZ to form a complex. Subsequent addition of PDDA causes the aggregation of 20-nm AuNPs which is accompanied by a color change from red to blue. Based on this color change, LZ can be determined qualitatively with bare eyes, and quantitatively by photometry by measuring the absorbance ratio at 590 and 531 nm. The calibration plot is linear in the 4.4 to 200 nM LZ concentration range, and the detection limit is 4.4 nM (at an S/N ratio of 3). The method was successfully employed to the determination of LZ in egg white. Results were compared to those of an established method and gave recoveries between 95.8 and 115 %, with RSDs of <3.9 %.
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