Chemometrics coupled 4-Aminothiophenol labelled Ag-Au alloy SERS off-signal nanosensor for quantitative detection of mercury in black tea.

Black tea like other food crops is prone to mercury ion (Hg2+) contamination right from cultivation to industrial processing. Due to the dangerous health effects posed even in trace contents, sensitive detection and quantification sensors are required. This study employed the surface-enhanced Raman scattering (SERS) enhancement property of 4-aminothiophenol (4-ATP) as a signal turn off approach functionalized on Ag-Au alloyed nanoparticle to firstly detect Hg2+ in standard solutions and spiked tea samples. Different chemometric algorithms were applied on the acquired SERS and inductively coupled plasma-mass spectrometry (ICP-MS) chemical reference data to select effective wavelengths and spectral variables in order to develop models to predict the Hg2+. Results indicated that Ag-Au/4-ATP SERS sensor combined with ant colony optimization partial least squares (ACO-PLS) exhibited the best correlation efficient and minimum errors for Hg2+ standard solutions (Rc = 0.984, Rp = 0.974, RMSEC = 0.157 µg/mL, RMSEP = 0.211 µg/mL) and spiked tea samples (Rc = 0.979, Rp = 0.963, RMSEC = 0.181 µg/g and RMSEP = 0.210 µg/g). The limit of detection of the proposed sensor was 4.12 × 10-7 µg/mL for Hg2+ standard solutions and 2.83 × 10-5 µg/g for Hg2+ spiked tea samples. High stability and reproducibility with relative standard deviation of 1.14% and 0.84% were detected. The potent strong relationship between the SERS sensor and the chemical reference method encourages the application of the developed chemometrics coupled SERS system for future monitoring and evaluation of Hg2+ in tea.

Signal-enhanced SERS-sensors of CAR-PLS and GA-PLS coupled AgNPs for ochratoxin A and aflatoxin B1 detection.

Ochratoxin-A (OTA) and aflatoxin-B1 (AFT-B1) pose debilitating health threats to consumers and therefore require rapid monitoring with sensors. This work synthesized silver nanoparticles (AgNPs) within (4 ≤ pH ≤ 11) ± 0.2 to attain different enhancement-factors (EF). AgNP@pH-11 which gave the highest SERS-EF (1.45 × 108) was selected to fabricate SERS-sensor; and coupled to two chemometric algorithms for the prediction of OTA and AFT-B1 in prepared standard solutions (SS) and spiked-cocoa-beans samples (SCBS). The LOD for OTA (2.63 pg/mL) and AFT-B1 (4.15 pg/mL) in the SCBS were lower compared with 0.002 µg/mL. The built-models recorded residual-predictive-deviations above 3. Obtained recovery rates of 96-110%; and the low coefficients of variation (2.12-8.07%) realized for both toxins suggest the predicted results are reproducible. The SERS-sensor holds promise for the rapid quantification of OTA and AFT-B1 at pg/mL level in cocoa beans to enable safety assurance in the cocoa beans industry.

NaYF4@Yb,Ho,Au/GO-nanohybrid materials for SERS applications-Pb(II) detection and prediction.

Nowadays, nano hybrid materials (NHMs) with latent applications have been employed in different fields, particularly for sensor applications. Among NHMs, GO based - upconversion NHMs system is an emerging area for the rapid detection of different hazardous materials either as an aptamer based or free-labeled sensing techniques. For the detection of Pb(II) in water, NaYF4@Yb,Ho,Au/GO-NaYF4@Yb,Ho,Au NHMs system was developed. The synthesized NHMs were characterized by XRD, FT-IR, SEM with EDS, TEM and Raman characterization techniques for observation and confirmation. NaYF4@Yb,Ho,Au/GO-NaYF4@Yb,Ho,Au NHMs fabricated sensors were observed to detect and quantify on real-time basis Pb(II) via surface-enhanced-Raman spectroscopy within the dynamic linear range of 98-99%, with detection limits of 1.16 × 10-9 g/mL and 1.15 × 10-8 g/mL obtained respectively for NaYF4@Yb,Ho,Au and GO- NaYF4@Yb,Ho,Au NHMs. The relative standard deviation (RSD) value achieved for both were less than ∼10%, indicative of reproducibility in the quantification results for Pb(II) traces in water when combined with genetic algorithm partial least square (GA-PLS). Results suggest that the GO-NHMs better enhanced the SERS Pb (II) vis-à-vis NaYF4@Yb,Ho,Au. The GO-wrapped NHMs exhibited a further better SERS performance because the heterostructure of GO-NHMs could be potentially useful for SERS-based immunoassay due to the much easier charge transfer between graphene and the metal ions and molecules so the homogeneity of the SERS probe was improved simultaneously (chemical enhancement) by GO-NHMs.