Gold nanoparticle core–europium(iii) chelate fluorophore-doped silica shell hybrid nanocomposites for the lateral flow immunoassay of human thyroid stimulating hormone with a dual signal readout

Abstract

Hybrid nanocomposite particles composed of a gold core coated with a europium(iii)-chelate fluorophore-doped silica shell (AuNPs@SiO-Eu) have been synthesized and applied as antibody labels in lateral flow immunoassay (LFIA) devices for the determination of human thyroid stimulating hormone (hTSH). Labeling of monoclonal anti-hTSH antibodies with AuNPs@SiO-Eu nanocomposites allows for both colorimetric and fluorometric observation of assay results on LFIA devices, relying on visible light absorption due to the localized surface plasmon resonance of the Au-core and the fluorescence emission of the Eu(iii)-chelate-modified shell under UV hand lamp irradiation (365 nm), respectively. The possibility for a dual signal readout provides an attractive alternative for LFIAs: instantaneous naked eye observation of the AuNP colorimetric signal as in conventional LFIAs for hypothyroidism detection, and more sensitive fluorescence detection to assess hyperthyroidism. The limits of detection (LOD) for naked eye observation of LFIA devices are 5 μIU mL and 0.1 μIU mL for the colorimetric and fluorimetric detection, respectively. Using the fluorescence detection scheme in combination with a smartphone and digital color analysis, a quantitative linear relationship between the red intensity and the logarithmic concentration of hTSH was observed (R = 0.988) with an LOD of 0.02 μIU mL. Finally, LFIA devices were effectively applied for detecting hTSH in spiked diluted human serum with recovery values between 100-116%.

Latest Trends in Lateral Flow Immunoassay (LFIA) Detection Labels and Conjugation Process

“…A physical adsorption conjugation method was used by Preechakasedkit et al (2018) , in which a hybrid nanocomposite consisting of an GNPs core and a europium (III) chelate fluorophore-doped silica shell (GNPs@SiO 2 -Eu 3+ ) was used as a detection label for human thyroid stimulating hormone (hTSH) assay. First, 1 ml of the nanocomposite suspended in 0.025 M carbonate buffer (pH 9.5) was mixed with 80 µg/ml anti-hTSH antibody for 12 h at 4°C, then 100 µl of a blocking solution containing 0.01 M PBS (pH 7.4), 2% (w/v) BSA and 4% (w/v) sucrose was added and stirred for 6 h at 4°C.…”

“…First, 1 ml of the nanocomposite suspended in 0.025 M carbonate buffer (pH 9.5) was mixed with 80 µg/ml anti-hTSH antibody for 12 h at 4°C, then 100 µl of a blocking solution containing 0.01 M PBS (pH 7.4), 2% (w/v) BSA and 4% (w/v) sucrose was added and stirred for 6 h at 4°C. The GNPs@SiO 2 -Eu 3+ -anti-hTSG conjugate was obtained after centrifugation at 8,000 g for 10 min and resuspension of the pellets in 100 µl of 0.01 M PBS (pH 7.4) containing 2% (w/v) BSA, 4% (w/v) sucrose and 0.05% (v/v) Tween 20 ( Preechakasedkit et al, 2018 ).…”

Recent Advances in Silica-Nanomaterial-Assisted Lateral Flow Assay

“…Taking advantage of the enhanced colorimetric and fluorescent signals of the labels, these novel LFA strips realized dual-signal qualitative sensing and a quantitative analysis of Cys C within 8 min. Preechakasedkit et al also developed a dual-model LFA by using hybrid nanocomposite materials (AuNPs@SiO 2 -Eu 3+ ) as the label [ 20 ]. A silica layer was created to protect the fluorescent Eu 3+ from environmental influence (e.g., photo-decomposition) and quenching by the Au core, resulting in a stability higher than that of free fluorophores.…”

“…In LFAs, silica nanomaterials usually work as a protective shell to stabilize label materials, a carrier to enrich label materials for signal amplification or the colored label itself. Reprinted with permission from References [ 20 , 21 , 22 , 23 ].…”

Development of a Prototype Lateral Flow Immunoassay of Cortisol in Saliva for Daily Monitoring of Stress

“…Researchers are developing immunochromatographic tests to identify pathogens [ 1 , 2 ] and markers of various diseases in humans [ 3 , 4 , 5 , 6 ], animals [ 7 ], and plants [ 8 ], pesticides [ 9 ], and toxins in water and food [ 10 ]. Immunochromatographic tests are also being developed to detect human hormones in order to assess health statuses [ 11 , 12 , 13 ].…”