Ultrafast point-of-care colorimetric detection of dengue using gold nanoparticles capped with β-cyclodextrin modified NS1 antibody

Herein, an ultrafast point-of-care detection of dengue using gold nanoparticles (AuNPs) modified with a Non-structural protein 1 (NS1) antibody was developed to reduce the death rate it causes. The process starts with synthesizing AuNPs using β-cyclodextrin (β-CDs) as reducing and stabilizing agents. Then, the surface of AuNPs was modified using 11-mercaptoundecanoid acid (MUA) 95%, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/<i>N</i>-(3-dimethylammopropyl)-NO-hydroxysuccinimide (NHS), followed by bioconjugation using NS1 antibody to increase their selectivity and specificity. Under optimal conditions (0.36 mM HAuCl₄ and 0.005 M β-CDs at pH 12), the AuNPs have a red wine color with an SPR absorption band at 517 nm with an absorbance of 0.636. After modification with NS1 antibody (AuNPs-mAb), the spectrum shifted to 522 nm with an absorbance of 0.044 and a slightly purplish color. The results showed that AuNPs-mAb can detect dengue virus in 1 minute (ultrafast). This can be seen from the absorbance change of 0.296, the wavelength shifted to 526 nm, and the color change of the solution from slightly purplish to faint purple. This method has high sensitivity with a correlation coefficient of 0.9992, and the Limit of Detection (LoD) and Limit of Quantitation (LoQ) values are 39 290 ng mL^-1 and 130 968 ng mL^-1, respectively, with a linear concentration range between 75-250 ng mL^-1. AuNPs-mAb also showed high selectivity to NS1 antigen at a 75 ng mL^-1 concentration compared to glucose, cholesterol, and uric acid at the same concentration. In addition, this method was proven effective when tested on human serum samples, showing excellent results in detecting dengue virus.