Sialic Acid-Functionalized Gold Nanoparticles for Sensitive and Selective Colorimetric Determination of Serotonin

Abstract

We present a novel colorimetric method inspired by nature's complex mechanisms, capable of selectively determining serotonin with high sensitivity. This method exploits the inherent binding affinity of serotonin with sialic acid (SA) molecules anchored to gold nanoparticles (SA-AuNPs). Upon serotonin binding, SA-AuNPs aggregate, and a characteristic red shift in the absorbance of SA-AuNPs accompanied by a dramatic color change (red to blue) occurs, readily observable even without instrumentation. The proposed method effectively eliminates interventions from potential interfering species such as dopamine, epinephrine, l-tyrosine, glucosamine, galactose, mannose, and oxalic acid. The absence of a color change with l-tryptophan, a structurally related precursor of serotonin, further confirms the high selectivity of this approach for serotonin detection. The colorimetric method has a wide linear dynamic range (0.05-1.0 μM), low limit of detection (0.02 μM), and fast response time (5 min). The limit of detection of the method is lower than other colorimetric serotonin sensors reported so far. The possible use of the proposed method in biological sample analysis was evaluated by employing a serotonin recovery assay in processed human plasma. The recoveries ranged from 90.5 to 104.2%, showing promising potential for clinical applications.

Figure 1

(a) TEM image, (b) SEM image, (c) EDX pattern, and (d) hydrodynamic size distribution graph of SA-AuNPs.

Figure 2

FT-IR spectrum of SA-AuNPs, and the scan number was 24.

Figure 3

Color scheme and the absorption spectra of the SA-AuNP solutions having pH values of 2.6, 3.0, 7.0, and 11.0.

Figure 4

Absorption spectra of SA-AuNP solutions without and with 1.0 and 300.0 μM serotonin concentrations at pH values of (a) 3.0, (b) 7.0, and (c) 11.0.

Figure 5

Absorbance ratio (A₆₅₀/A₅₂₀) was measured at different temperatures after the addition of 1.0 μM serotonin at pH 3.0, and the standard deviation was based on three measurements.

Figure 6

Time dependence of the absorbance ratio (A₆₅₀/A₅₂₀), the standard deviation was based on three measurements.

Figure 7

(a) Scheme for serotonin and SA-AuNPs interaction; (b) visual color change of SA-AuNP solutions after addition of serotonin standard solutions (2–12) and color of blank solution (1); (c) calibration plot of serotonin standard solutions (2–12) between 0.05 and 1.0 μM.

Figure 8

(a) Absorption spectra of SA-AuNPs and (b) the difference between the absorbance ratio of SA-AuNPs at 650–520 nm before and 5 min after the addition of serotonin and interfering species to the SA-AuNP solution.