Label-free

The label-free detection of biomolecules is another promising field of application for SERS spectroscopy. Tiniest amounts of these molecules can be adsorbed by specific interactions with receptors immobilized on SERS-active surfaces. They can then be identified by their spectra, or specific interactions can be distinguished from unspecific interactions by monitoring characteristic changes in the conformation sensitive SERS spectra of the receptors. 

The ion-triplet oxidises I in the slow step to yield -Iz . The non-participation of any ligand substitution step is confirmed by the absence of any incorporation of activity from added C-labelled free cyanide ion into the product ferrocyanide ... 

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Birkert O., Tunnemann R., Jung G., Gauglitz G., Label-Free Parallel Screening of Combinatorial Triazine Libraries Using Reflectometric Interference Spectroscopy, Anal Chem 2002 74 834. 

Birkert O., Gauglitz G., Development of an assay for label-free high-throughput screening of thrombin inhibitors by use of reflectometric interference spectroscopy, AnalBioanal Chem 2002 372 141-147. 

Kroger K., Bauer J., Fleckenstein F., Rademann J., Jung G. and Gauglitz G., Epitopemapping of transglutaminase with parallel label-free optical detection, Biosens Bioelectron 2002 17 937-944. 

Sauer M., Brecht A., Charisse K., Stemmier I., Gauglitz G. and Bayer E., Interaction of Chemically Modified Antisense Oligonucleotides with Sense DNA A Label-Free Interaction Study with Reflectometric Interference Spectroscopy, Anal Chem 1999 71 2850. 

Cottier K., Wiki M., Voirin G., Gao H., Kunz R.E., Label-free highly sensitive detection of (small) molecules by wavelength interrogation of integrated optical chips, Sens. andActuat. 5.2003 91 241-251. 

Kanda V, Kariuki JK, Harrison DJ, McDermott MT (2004) Label-free reading of microarray-based immunoassays with surface plasmon resonance imaging. Anal Chem 76 7257-7262... 

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Maehashi, K., Katsura, T., Kerman, K., Takamura, Y., Matsumoto, K., and Tamiya, E. (2007) Label-free protein biosensor based on aptamer-modified carbon nanotube field-effect transitors. Anal. Chem. 79, 782-787. 

J. Horacek and P. Skladal, Improved direct piezoelectric biosensors operating in liquid solution for the competitive label-free immunoassay of 2,4-dichlorophenoxyacetic acid. Anal. Chim. Acta 347, 43-50 (1997). 

S. Grant, F. Davis, K.A. Law, A.C. Barton, S.D. Collyer, S.P.J. Higson, and T.D. Gibson, Label-free and reversible immunosensor based upon an AC impedance interrogation protocol. Anal. Chim. Acta 537, 163-168 (2005). 

The results obtained with PE multilayers as well as DNA on top of the capacitive EIS sensor could verify their feasibility as transducer for a label-free detection of adsorption, binding, and interactions of charged macromolecules. Nevertheless, our experiments do not enable us to clearly distinguish between the contributions in the signal generation from each of the mechanisms discussed in sections 7.3 and 7.4. Probably, both basic mechanisms, namely, the intrinsic charge of molecules and the ion-concentration redistribution in the intermolecular spaces or in the multilayer, affect the sensor signal by superposition. 

At the same time, however, it must be concluded that the practical development of FEDs for a label-free detection of DNA and other charged macromolecules by their intrinsic molecular charge seems to be more complicated than originally expected. Although the discussed results are highly exciting, they are rather diverse and even sometimes inconsistent. Factors influencing the DNA immobilization and hybridization detection by FEDs are ... 

D. Goncalves, D.M.F. Prazeres, V. Chu, and J.P. Conde, Label-free electronic detection of biomolecules using a-Si H field-effect devices. J. Non-Crystalline Solids 352, 2007-2010 (2006). 

MJ. Schoning, M.H. Abouzar, S. Ingebrandt, J. Platen, A. Offenhauser, and A. Poghossian, Towards label-free detection of charged macromolecules using field-effect-based structures scaling down from capacitive EIS sensor over ISFET to nano-scale devices, in Mater. Res. Soc. Symp. Proc. 915, 0915-R05-04 (2006). 

A. Poghossian, A. Cherstvy, S. Ingebrandt, A. Offenhauser, and M. J. Schoning, Possibilities and limitations of label-free detection of DANN hybridisation with field-effect-based devices. Sens. Actuators B 111, 470-480 (2005). 

Z.H. Wang and G. Jin, A label-free multisensing immunosensor based on imaging ellipsometry. Anal. Chem. 75, 6119-6123 (2003). 

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