Extrinsic detection

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)... 

Ideal Performance and Cooling Requirements. Eree carriers can be excited by the thermal motion of the crystal lattice (phonons) as well as by photon absorption. These thermally excited carriers determine the magnitude of the dark current,/ and constitute a source of noise that defines the limit of the minimum radiation flux that can be detected. The dark carrier concentration is temperature dependent and decreases exponentially with reciprocal temperature at a rate that is determined by the magnitude of or E for intrinsic or extrinsic material, respectively. Therefore, usually it is necessary to operate infrared photon detectors at reduced temperatures to achieve high sensitivity. The smaller the value of E or E, the lower the temperature must be. 

Fig. 9. Spectral sensitivity of detectors where the detector temperatures in K are in parentheses, and the dashed line represents the theoretical limit at 300 K for a 180° field of view, (a) Detectors from near uv to short wavelength infrared (b) lead salt family of detectors and platinum siUcide (c) detectors used for detection in the mid- and long wavelength infrared. The Hg CdTe, InSb, and PbSnTe operate intrinsically, the doped siUcon is photoconductive, and the GaAs/AlGaAs is a stmctured supedattice and (d) extrinsic germanium detectors showing the six most popular dopants.

As femtomolar detection of analytes become more routine, the goal is to achieve attomolar (10 molar) analyte detection, corresponding to the detection of thousands of molecules. Detection sensitivity is enhanced if the noise ia the analytical system can be reduced. System noise consists of two types, extrinsic and intrinsic. Intrinsic aoise, which represents a fundamental limitation linked to the probabiHty of finding the analyte species within the excitation and observation regions of the iastmment, cannot be eliminated. However, extrinsic aoise, which stems from light scatteriag and/or transient electronic sources, can be alleviated. 

Our results also shed light on the long-lived PA3 band detected in transient PM measurements of P3BT (see Fig. 7-19) and can explain changes in the PA spectra observed in several ps transient measurements of films of PPV derivatives at energies around 1.8 eV [9, 25, 60J. In good PPV films the transient PA spectrum shows a PA band of excitons at 1.5 eV whose dynamics match those of the PL and stimulated emission (SE) [9J. However, in measurements of oxidized [25] or C60-doped films 60, there appears a new PA band at about 1.8 eV whose dynamics are not correlated with those of the PL and SE. Based on our A-PADMR results here, we attribute the new PA band at 1.8 eV to polaron pair excitations. These may be created via exciton dissociation at extrinsic defects such as carbo-... 

The fast, sensitive, reliable, and reproducible detection of (bio)molecules including quantification as well as biomolecule localization, the measurement of their interplay with one another or with other species, and the assessment of biomolecule function in bioassays as well as in vitro and in vivo plays an ever increasing role in the life sciences. The vast majority of applications exploit extrinsic fluorophores like organic dyes, fluorescent proteins, and also increasingly QDs, as the number of bright intrinsic fluorophores emitting in the visible and NIR is limited. In the near future, the use of fluorophore-doped nanoparticles is also expected to constantly increase, with their applicability in vivo being closely linked to the intensively discussed issue of size-related nanotoxicity [88]. 

Extrinsic fluors are produced via a chemical reaction where the added reagent either enhances emission of a weak emitter through association or the analyte is derivatized with a fluor tag. 8-Hydroxyquinoline (HQS) is an example of an extrinsic complexing reagent (Reaction 11.1) where the native ligand is a marginal fluorophore but forms intense emitting metal chelates. This approach affords sensitive detection of... 

Fluoroimmunoassays comprise a subclass of extrinsic labehng methods where various selective antigen (Ag)- antibody (Ab) immunoassay fluorescent labeling schemes yield a emission signal. One common scheme involves an enzyme-linked immunosorbent assay (ELISA) depicted in Figure 11.2 where the free Ab is tagged with a fluorophore. Numerous analytes can be detected via these types of selective lock-and-key methods. ... 

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. ... 

---