Visual detection of tropomyosin, a major shrimp allergenic protein using gold nanoparticles (AuNPs)-assisted colorimetric aptasensor

Abstract

A gold nanoparticle-based label-free colorimetric assay was developed to detect the shrimp allergenic protein tropomyosin (TM), an important biomarker responsible for severe clinical reactivity to shellfish. In a gold nanoparticles (AuNPs)-tropomyosin-binding aptamer (TMBA) complex, the aptamer adsorbs onto the surface of AuNPs and dissociates in the presence of TM. In addition, AuNPs tend to aggregate in the presence of ionic salt, revealing a color change (i.e., wine-red to purple/blue) with a shift in the maximum absorption peak from 520 nm. In the presence of specific binding TM, the aptamer folds into a tertiary structure where it more efficiently stabilizes AuNPs toward the salt-induced aggregation with a hypsochromic shift in the absorption spectra compared to the stabilized AuNPs by aptamer alone. Based on the aggregation and sensitive spectral transformation principle, the AuNPs-based colorimetric aptasensor was successfully applied to detect TM with a range of 10-200 nmol/L and a low detection limit of 40 nmol/L in water samples. The reliability, selectivity, and sensitivity of the aptasensor was then tested with food samples spiked with TM. The observed detection limit was as low as 70 nmol/L in shrimp, 90 nmol/L in tofu, and 80 nmol/L in eggs, respectively. We anticipate the proposed AuNPs-based colorimetric aptasensor assay possesses a high potential for the easy and efficient visual colorimetric detection of TM.

Supplementary information: The online version contains supplementary material available at 10.1007/s42995-020-00085-5.

Keywords: Aggregation; Aptamer; Colorimetric assay; Gold nanoparticles (AuNPs); Shellfish allergenic protein; Shrimp tropomyosin (TM).

Fig. 1

a UV–visible absorption spectrum of gold nanoparticles (AuNPs); b TEM image of citrate-stabilized gold nanoparticles (AuNPs); and c typical wine red color of the colloidal AuNPs

Fig. 2

a Interaction of tropomyosin binding aptamer (TMBA) and target protein tropomyosin (TM) with gold nanoparticles (AuNPs) observed at 520 nm maximum absorbance wavelength and b interaction of aptamer and its target protein with AuNPs via UV–visible Spectroscopy

Fig. 3

Gold nanoparticles (AuNPs) aggregation phenomenon a UV–Vis spectra and b naked eye with TEM

Fig. 4

Investigation of gold nanoparticles-tropomyosin (AuNPs-TM) interaction/binding via induced aggregation a UV–Vis spectroscopy; b visual colorimetric salt-induced aggregation of AuNPs-TM (at various concentration of TM); and c visual colorimetric salt-induced aggregation of AuNPs-TM and AuNPs-control allergenic proteins at 100 nmol/L NaCl concentration

Fig. 5

Mechanism of tropomyosin binding aptamer (TMBA) adsorption onto AuNPs with/without NaCl induced aggregation; a colorimetric investigation; and b UV–vis spectroscopy

Fig. 6

Determination of tropomyosin (TM) using AuNPs-TMBA complex via salt-induced aggregation a UV–Vis spectroscopy of AuNPs-TMBA-TM-NaCl and b visual colorimetric representation of TM recognition via induced aggregation

Fig. 7

AuNPs-aptamer based colorimetric sensor array: selectivity and sensitivity of tropomyosin (TM) detection

Fig. 8

Colorimetric detection of tropomyosin (TM) in real food samples a visual naked eye detection and b–d UV–Vis spectroscopy of real food samples for recognition of TM via salt-induced aggregation of AuNPs

Fig. 9

Selectivity validation of AuNPs-aptamer colorimetric sensor array a colorimetric visual observation and b UV–visible spectroscopy of control proteins spiked food samples