The efficiency analysis of gold nanoprobes by FT-IR spectroscopy applied to the non-cross-linking colorimetric detection of Paracoccidioides brasiliensis

Nanodiagnostics have become an important tool for the development of new methods for clinical and laboratory diagnosis. Non-cross-linking colorimetric detection is a promising technique using thiol-modified oligonucleotides (probes) functionalized gold nanoparticles. The nanoprobes allow the detection of a specific sequence of complementary DNA (cDNA) for a well-characterized antigenic protein 27 kDa (p27), which is capable of reacting with the serum of 91% of the patients infected with fungus Paracoccidioides brasiliensis the etiologic agent of Paracoccidioidomycosis. In this work nanoprobe groups were synthesized with final concentration of 33.6 nM, 66.1 nM and 128.1 nM thiolated oligonucleotides. To evaluate the efficiency of the nanoprobes Fourier Transform Infrared (FT-IR) was used to identify the functional groups of the probe and its bond to the gold nanoparticle. The region between 200 cm−1 and 280 cm−1 corresponds to the AuS bond, which is a determining factor for the efficiency of colorimetric detection. The FT-IR results are corroborated with images taken with the Transmission Electron Microscopy (TEM) technique, where the difference between functionalization groups is evident. Considering these aspects, the present work aims to develop a new molecular diagnosis of the fungus Paracoccidioides brasiliensis by non-cross-linking colorimetric detection method using a probe from p27 antigenic cDNA sequence. The non-cross-linking colorimetric diagnostic test possesses 84.4% sensitivity and 81.2% specificity, and may be implemented as clinical diagnosis with simple execution and reasonable cost to effectively detect of Paracoccidioides brasiliensis.