Intrinsic detection

The detection limits, accuracy, and precision of any analytical methodology, as well as the composition of the sample medium, are important parameters in determining the appropriateness of a method to quantify a specific analyte at the desired level of sensitivity within a particular matrix. The lower limit of detection (LLD) has been adopted to refer to the intrinsic detection capability of a measurement procedure (sampling... 

At-line LIF methods are either based on intrinsic detection or extrinsic approaches. The former often involves static measurements which are prone to photobleaching and thermal effects. These problems can often be addressed by optimizing the excitation source output (i.e., optical power and pulse rate) or by sample agitation. Flow injection analysis or other autonomous sample prepreparation schemes are possible to facilitate various at-line extrinsic methods such as various selective fluoroimmunoassays. ... 

Problem 3.4 Positrons in a 5mm-diameter beam are detected in two different ways (a) directly by a channeltron (lOmm-diameter mouth) placed at the end of an evacuated beam line, and (b) indirectly via annihilation radiation from the channeltron by a 75mm-diameter, 75mm-long Nal(Tl) crystal on a PM detector mounted outside the vacuum system directly to one side of the channeltron. The distance from the channeltron to the front face of the scintillator is 100mm, and the intrinsic detection efficiency of the... 

Ffe. 5.1 Schematic illustration of different approaches for SERS biomolecular detection, a Intrinsic detection of biomolecule (protein), b Extrinsic detection of labelled biomolecule (DNA). c Extrinsic detection of biomolecule using SERS tag (metallic NP with RRM). d SERS tag (metallic NP with RRMs, protective shell and antibody) for immunoassay (adapted from Wang et al. 2013. Copyright 2012 American Chemical Society)... 

In the case of intrinsic detection, the analyte can be directly applied to the nano-structured surfaces and the inherent Raman spectrum of the biomolecule directly measured to identify the specimen. In order to allow for capture and to aid the specificity of detection, antibodies, aptamers or related molecules can be immobilized onto nanostructured surfaces, as shown in Figure 5.15b the Raman spectral differences before and after capture of the specimen can then be used to identify the species. 

A number of physical devices with chemical sensitivity have been developed previously, including the quartz crystal microbalance (QCM) and other acoustic wave devices, semiconductor gas sensors, and various chemically sensitive field effect transistors. However, based on their intrinsic detection principles, most of the known solid state chemical sensors are not selective, i.e., they respond to more than one or a few chemical species. There is an urgent demand for new families of selective, microscope sensors that can eventually be integrated into microelectronic circuits. We have embarked on a program aimed at the design of conceptually new microporous thin films with molecular recognition capabilities. On the surface of chemical sensors, these membranes will serve as "molecular sieves that control access of selected target molecules to the sensor surface. 

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