CEQUINOR   05415
CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Study on the detection of cocaine in banknotes by SERS
Autor/es:
CARLOS O. DELLA VÉDOVA; ROSANA M. ROMANO; A. LORENA PICONE
Lugar:
Belém do Pará
Reunión:
Encuentro; VI Encontro Brasileiro de Espectroscopia Raman; 2019
Institución organizadora:
Universidad Federal do Pará
Resumen:
In recent years, Raman spectroscopy intensified by surface phenomena (SERS) has emerged as a very promising methodology for the qualitative and quantitative determination of different substances, reaching low detection limits and simplifying sample pre-treatments. In this context, our group has developed flexible SERS platforms, based on silver nanoparticles immobilized in an agar gel, to be used in the in-situ determination of different molecules (for example pesticides and drugs).In this study we explore the possibility to detect cocaine in banknotes using the agar developed platforms and SERS spectroscopy.First, the SERS substrates were prepared and their efficiency to act as SERS platforms for the detection of cocaine was compared with the use of commercial ones. Two different silver nanoparticles (NPs) were obtained in this work, following the preparation of Lee-Meisel1 and Zamborini,2 respectively. The average size of the nanoparticles was 25 (Lee-Meisel NPs) and 50 nm (Zamborini NPs) as determined by UV-visible spectroscopy and STEM. Each type of Ag NPs was subsequently immobilized in agar, which were characterized by Diffuse Reflectance UV-visible spectroscopy.10, 20 or 30 L of solutions prepared from pure cocaine samples either in ethanol or methanol of different concentration were sow over 1 cm2 of the SERS platforms. The substrates were allowed to dry for 24 hours before carrying out the measurements. The Raman spectra were taken with a Horiba Jobin Yvon T64000 spectrometer with confocal microscopy and a cryogenic CCD detector. Lines of 514.5 or 647.1 nm from Ar+ and Kr+ lasers, respectively, were employed for the excitation. In most of the measurements a 50x objective was used, and the power on the sample was ~1.5 mW. The band around 1003 cm-1, characteristic for the SERS spectrum of cocaine, was employed to align the sample and maximize each spectrum.The minimum quantities detected, expressed as g/cm2, were: 3.4 (commercial Ocean Optics RAM-SERS- SP (Au y Ag) platform), 0.1 (Lee-Meisel NPs in agar) and 0.3 (Zamborini NPs in agar). Mappings over each surface were also performed.Argentinean banknotes of $ 100 were contaminated with 20 L of the cocaine solutions in a 1 cm2 region. After the solvent was completely dry, the residue over the banknote surface was extracted with another 20 L of ethanol by rubbed on the banknote surface with the agar gel for approximately 15 s, as depicted in Figure 1.The SERS spectra of cocaine were detected, although, depending on the region of the banknote contaminated, the Raman spectrum presents fluorescence, thus decreasing the detection limits. The extraction process was repeated until no signals of the analyte were detected in the SERS spectra.The designed SERS platforms showed a very good SERS capacity for the cocaine analyte, better than the performance of the commercial substrate used for its evaluation. The potentiality of this methodology to perform in-situ determinations on banknotes was also demonstrated.