Signal enhancement, trace

The extremely small cross sections for conventional Raman scattering, typically 10 111 to 10-25 cm2/molecule has in the past precluded the use of this technique for single-molecule detection and identification. Until recently, optical trace detection with single molecule sensitivity has been achieved mainly using laser-induced fluorescence [14], The fluorescence method provides ultrahigh sensitivity, but the amount of molecular information, particularly at room temperature, is very limited. Therefore, about 50 years after the discovery of the Raman effect, the novel phenomenon of dramatic Raman signal enhancement from molecules assembled on metallic nanostructures, known as surface-enhanced Raman spectroscopy or SERS, has led to ultrasensitive single-molecule detection. 

Xie Z, Westmoreland SV, Bahn ME, Chen GL, Yang H, VaUender EJ, Yao WD, Madras BK, Miller GM (2007) Rhesus monkey trace amine-assodated receptor 1 signaling enhancement by monoamine transporters and attenuation by the D2 autoreceptor in vitro. J Pharmacol Exp Ther 321 116-127... 

Because of the huge signal enhancement, SERS is particularly useful for trace analysis and for in-situ investigations of various interfacial processes or of mono-layers adsorbed on metals. However, sample preparation is a rather tedious procedure. For this reason, SERS is still more an academic tool rather than a routine analytical instrument. Some applications of SERS are given in [31]. 

As with RRS, but with less fluorescence problems, the signal-enhancement factors (up to 10 ) afforded by surfaced-enhanced Raman scattering has proven to be useful in studies that required trace-level detection limits and high selectivity. Detection limits in the pi-cogram level and dynamic ranges over two to three orders of magnitude are often achieved (see Table 1). Note that, however, because the analyte signal for trace levels from NRS cannot be detected, actual enhancement factors are difficult to determine for most compounds. 

Minimisation of sample matrix effects and signal enhancement for trace analytes using anodic stripping voltammetry with detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 5(6), 437-445. 

Pretty, J. R., Evans, E. H., Blubaugh, E. A., Shen,W.-L., Caruso, J. A., and Davidson,T. M. (1990). Minimisation of sample matrix effects and signal enhancement for trace analytes using anodic stripping voltammetry with detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 5(8), 710. 

Figure 7. Time-of-flight mass spectra showing results of platinun cluster reactions with benzene. The lower trace is clean metal without reactant. The upper trace is with the pulsed addition of. 21 % benzene in heliun. The notation indicates the nmber of adducts on each metal cluster. The metal cluster are all two photon ionized, while the observed products are single photon ionized, hence the enhancement of the product over metal signals. Reproduced from Ref. 17.

The explanation of this result is illustrated in Fig. 1.37, which shows selected reaction-monitoring traces of the sample at 10 ng mL f It becomes obvious that the response ratio between the analyte and the IS has dramatically changed. On one side there is enhancement of the analyte s response and on the other side suppression of the internal standard (IS) signal. These effects are mainly caused... 

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