Teste colorimétrico portátil para detecção de DNA de Candida auris utilizando nanopartículas de ouro

Abstract

The emergence of Candida auris, a multidrug-resistant fungal pathogen, represents a serious global public health threat. Due to its ability to cause invasive infections and spread in hospital environments, rapid and accurate diagnosis is essential for outbreak control. This study aimed to develop and validate a portable, low-cost, and highly sensitive colorimetric test for the detection of C. auris DNA using gold nanoparticles (AuNPs). The method involved the synthesis of AuNPs by sodium citrate reduction, resulting in spherical nanoparticles with a characteristic absorption peak at 520 nm. The assay was optimized for a hybridization temperature of 55 °C, which proved ideal for the specific binding of the probe to the target DNA. The detection mechanism is based on the stabilization of AuNPs through hybridization with the target DNA, which prevents salt-induced aggregation and maintains the pink color of the solution. In the absence of the positive target, the nanoparticles aggregate, causing a clear color change to blue. This color shift was quantitatively confirmed by UV-Vis spectrophotometry, which demonstrated a distinct red-shift of the absorption peak in the negative controls. The sensitivity of the test was validated by the absence of response to HIV DNA, while the construction of a calibration curve demonstrated that the lowest detectable concentration was 1×10⁻⁹ mol/L of C. auris target DNA, indicating the potential of the assay for quantitative applications and for estimating fungal load in clinical samples. The specificity test evaluated non-complementary gRNA sequences from Zika and Hepatitis C viruses, as well as HIV DNA, in order to assess the system’s response. Additionally, a competitive assay with the same negative controls confirmed the system’s selectivity and robustness, without any interference in the detection of the positive target. In summary, the developed colorimetric test represents a promising tool for the rapid and accessible diagnosis of C. auris, making a significant contribution to surveillance and control of this important pathogen’s spread, especially in point-of-care (POC) settings.