Enhancing Surface Enhanced Raman Scattering (SERS) Detection of Propranolol with Multiobjective Evolutionary Optimization

Colloidal-based surface-enhanced Raman scattering (SERS) is a complex technique, where interaction between multiple parameters, such as colloid type, its concentration, and aggregating agent, is poorly understood. As a result SERS has so far achieved limited reproducibility. Therefore the aim of this study was to improve enhancement and reproducibility in SERS, and to achieve this, we have developed a multiobjective evolutionary algorithm (MOEA) based on Pareto optimality. In this MOEA approach, we tested a combination of five different colloids with six different aggregating agents, and a wide range of concentrations for both were explored; in addition we included in the optimization process three laser excitation wavelengths. For this optimization of experimental conditions for SERS, we chose the β-adrenergic blocker drug propranolol as the target analyte. The objective functions chosen suitable for this multiobjective problem were the ratio between the full width at half-maximum and the half-maximum intensity for enhancement and correlation coefficient for reproducibility. To analyze a full search of all the experimental conditions, 7785 experiments would have to be performed empirically; however, we demonstrated the search for acceptable experimental conditions of SERS can be achieved using only 4% of these possible experiments. The MOEA identified several experimental conditions for each objective which allowed a limit of detection of 2.36 ng/mL (7.97 nM) propranolol, and this is significantly lower (>25 times) than previous SERS studies aimed at detecting this β-blocker

Calibration curve for LC-MS.

<p>The curve was built from 20 different gradient concentrations of trimethoprim; see Supporting <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200272#pone.0200272.s001" target="_blank">S1 Text</a> for information on the concentrations of trimethoprim used to construct the standard curve.</p

PC-DFA score plots of GC-MS profiles.

<p>25 PCs were extracted from PCA and used as inputs to DFA, explaining 99% of the TEV. The legend in the figure shows the 95% CI for the correct classification of the 8 conditions. Significantly altered metabolites were mined through a combination of PC-DFA loadings and univariate significance testing (Student <i>t</i>-test). C, control.</p

Growth curves of <i>E</i>. <i>coli</i> K-12.

<p>(a) Growth curves of <i>E</i>. <i>coli</i> K-12 in three different media. Media: the blue plot indicates LB; red, NB and green, Ψ. (b) Growth curves of E. coli K-12 at four different pH values in the same LB medium. The blue plot indicates pH 3; red pH5; green pH 7 and purple pH 9. Six replicate growth curves were conducted and a typical growth curve for each condition is shown; the other five growth curves showed similar dynamics.</p

Metabolic effects of trimethoprim challenge on <i>E</i>. <i>coli</i> K-12 at pH 5 and pH 7.

<p>When partially ionized at pH 7, trimethoprim is seen to impact on metabolism directly associated with the dihydrofolate pathway, as well as off-target effects upon nucleotide, sugar and amino acid metabolism, glycolysis, the TCA cycle, and up-regulation of osmoprotectants. When trimethoprim is in a poorly ionized state (pH 5), it appears to have a profound effect upon the up-regulation of amino acid metabolism.</p

Optimization of Parameters for the Quantitative Surface-Enhanced Raman Scattering Detection of Mephedrone Using a Fractional Factorial Design and a Portable Raman Spectrometer

A new optimization strategy for the SERS detection of mephedrone using a portable Raman system has been developed. A fractional factorial design was employed, and the number of statistically significant experiments (288) was greatly reduced from the actual total number of experiments (1722), which minimized the workload while maintaining the statistical integrity of the results. A number of conditions were explored in relation to mephedrone SERS signal optimization including the type of nanoparticle, pH, and aggregating agents (salts). Through exercising this design, it was possible to derive the significance of each of the individual variables, and we discovered four optimized SERS protocols for which the reproducibility of the SERS signal and the limit of detection (LOD) of mephedrone were established. Using traditional nanoparticles with a combination of salts and pHs, it was shown that the relative standard deviations of mephedrone-specific Raman peaks were as low as 0.51%, and the LOD was estimated to be around 1.6 μg/mL (9.06 × 10^–6 M), a detection limit well beyond the scope of conventional Raman and extremely low for an analytical method optimized for quick and uncomplicated in-field use

Growth characteristics of <i>E</i>. <i>coli</i>.

<p>(a) Growth curves of <i>E</i>. <i>coli</i> K-12 at pH 5 (dashed line) and pH 7 (solid line). For pH 5, the dashed blue line represents control samples, dashed red indicates samples challenged with 0.8 mg L^-1 of trimethoprim added at the beginning of the lag phase (t = 0 h) and dashed green denotes samples challenged with 0.8 mg L^-1 of trimethoprim and added at mid-exponential phase (t = 5 h). For pH 7, the solid purple line represents control samples, solid light blue indicates samples challenged with 0.8 mg L^-1 of trimethoprim added at the beginning of the lag phase (t = 0 h) and solid orange denotes samples challenged with 0.8 mg L^-1 of trimethoprim and added at the exponential phase (t = 5 h). (b) Column chart representing relative <i>E</i>. <i>coli</i> intracellular levels of trimethoprim after challenging with 0.8 mg L^-1 of the drug at pH 5 (red columns) and pH 7 (blue columns) at different growth stages (time = 0 and 5 h) as detected by LC-MS analysis after cells were grown for a total of 18 h. Six replicate growth curves were conducted and a typical growth curve for each condition is shown; the other five growth curves showed similar dynamics.</p

PCA and DFA on FT-IR spectra reveal pH and trimethoprim effects.

<p>(a) PCA scores plot of PC1 <i>vs</i>. PC2 after CO₂ removal around 2350 cm^-1 and EMSC scaling. The total explained variance (TEV) of PC1 is 78.9% and for PC2 is 12.8%. (b) PC-DFA score plots of pH 5 and 7 samples. 20 PCs were extracted from PCA and used as inputs to DFA. These 20 PCs explain 99% of TEV; the legend in the plot shows the 95% confidence interval (CI) for the correct classification of the eight conditions. C, control.</p

Optimization of Parameters for the Quantitative Surface-Enhanced Raman Scattering Detection of Mephedrone Using a Fractional Factorial Design and a Portable Raman Spectrometer

A new optimization strategy for the SERS detection of mephedrone using a portable Raman system has been developed. A fractional factorial design was employed, and the number of statistically significant experiments (288) was greatly reduced from the actual total number of experiments (1722), which minimized the workload while maintaining the statistical integrity of the results. A number of conditions were explored in relation to mephedrone SERS signal optimization including the type of nanoparticle, pH, and aggregating agents (salts). Through exercising this design, it was possible to derive the significance of each of the individual variables, and we discovered four optimized SERS protocols for which the reproducibility of the SERS signal and the limit of detection (LOD) of mephedrone were established. Using traditional nanoparticles with a combination of salts and pHs, it was shown that the relative standard deviations of mephedrone-specific Raman peaks were as low as 0.51%, and the LOD was estimated to be around 1.6 μg/mL (9.06 × 10^–6 M), a detection limit well beyond the scope of conventional Raman and extremely low for an analytical method optimized for quick and uncomplicated in-field use

Growth, survival and extension of lag phase in X-irradiated cultures of <i>S</i>. <i>oneidensis</i> MR-1.

<p>(A) Growth profiles of aerobic cultures of <i>S</i>. <i>oneidensis</i> MR-1 (30°C) after exposure to 12, 24, 48, 72 and 95 Gy X-radiation (0.79 Gy min^-1). Irradiations began at t = 0. A minimal growth medium was used, based on that described previously [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131249#pone.0131249.ref032" target="_blank">32</a>]. Data points show mean of triplicate batch cultures and error bars depict 95% confidence intervals. (B) Mean time difference in lag phase duration between irradiated cultures and respective controls (measured at mid exponential phase). Error bars depict 95% confidence intervals from three biological replicates. (C) Survival of <i>S</i>. <i>oneidensis</i> MR-1 exposed to acute doses of X-radiation. Cultures were irradiated in the growth medium described above, serially diluted in phosphate buffered saline and plated on to solid growth medium (same as above with 1.5% agar). Error bars depict standard error of the mean CFU mL^-1.</p