Colorimetric, Naked-Eye Detection of Lysozyme in Human Urine with Gold Nanoparticles

Abstract

The stabilizing effect of lysozymes to salt addition over a gold colloid are exploited in order to detect lysozymes in human urine samples. The present research is aimed at the development of a fast, naked-eye detection test for urinary lysozymuria, in which direct comparison with a colorimetric reference, allows for the immediate determination of positive/negative cases. CIEL*a*b* parameters were obtained from sample absorbance measurements, and their color difference with respect to a fixed reference point was measured by calculating the ΔE₇₆ parameter, which is a measure of how well the colors can be distinguished by an untrained observer. Results show that a simple and quick test can reliably, in less than 15 min, give a positive colorimetric response in the naked eye for concentrations of a urinary lysozyme over 57.2 µg/mL. This concentration is well within the limits of that observed for leukemia-associated lysozymurias, among other disorders.

Keywords: CIELab; colorimetry; gold nanoparticles; lysozyme; lysozymuria; naked-eye detection; proteinuria; urine.

Scheme 1

Protective effect of lysozyme upon NaCl addition over citrate-capped gold nanoparticles.

Scheme 2

Schematic representation of the three CIEL*a*b* color system axes.

Figure 1

(a) Absorbance spectrum and (b) TEM imaging of the nanoparticle synthesis employed for working tests. Scale bar corresponds to 200 nm.

Figure 2

Normalized absorbance spectra for different concentrations of a urinary lysozyme. Series correspond to sample 1.

Figure 3

Preliminary naked-eye tests for lysozyme concentrations ranging from 143.1 to 0.71 µg/mL.

Figure 4

RGB color simulation obtained from experimental L*a*b* parameters corresponding to different lysozyme concentrations in urine. Blank samples have no urine and no lysozyme.

Figure 5

Sample-blank color difference ΔE₇₆ evolution with increasing lysozyme concentrations. Error bars, derived from repeated measurements, are shown for Sample 1.

Figure 6

Normalized absorbance spectra for different concentrations of urinary lysozyme. Series correspond to sample F.

Figure 7

RGB color simulation obtained from experimental L*a*b* parameters corresponding to different lysozyme concentrations in urine.

Figure 8

Mean color difference ΔE₇₆ evolution for samples A–J with increasing lysozyme concentrations.