Biochips labeling

Based on IgG-bearing beads, a chemiluminescent immuno-biochip has been also realized for the model detection of human IgG. Biotin-labeled antihuman IgG were used in a competitive assay, in conjunction with peroxidase labelled streptavidin59. In that case, the planar glassy carbon electrode served only as a support for the sensing layer since the light signal came from the biocatalytic activity of horseradish peroxidase. Free antigen could then be detected with a detection limit of 25 pg (108 molecules) and up to 15 ng. 

In a similar way, the use of oligonucleotide-immobilized beads enabled the realization of DNA sensitive biochips that could be used to detect biotin labelled sequence as 5.108 molecules59. 

In conventional chip experiments, fluorescence scanners are used for chip read-out. In the case of laser scanners, HeNe lasers are used as excitation sources and photomultiplier tubes as detectors, whereas CCD-based scanners use white light sources. The optical system can be confocal or non-confocal. Standard biochip experiments are performed using two fluorescent labels as... 

An array or a matrix of nucleic acid probes immobilized at discrete locations on a silicon or glass surface provides a convenient means to simultaneously probe a sample for the presence of many different target sequences. Microarray biochip scanning devices, mostly based on fluorescent labels, are now currently available, and could also be used with CL labels to take advantage of the higher sensitivity of this detection principle. 

The origin of the microarray or biochip can be traced to a seminal publication by Edwin Southern over 30 years ago. Southern described a method by which DNA could be attached to a solid support following electrophoresis and interrogated for sequences of interest by hybridization with a complementary DNA sequence (16). The complementary DNA sequence, termed a probe, was labeled with either a radioactive or a fluorescent marker and hybridized to the DNA target sample, which was immobilized on a sohd support, such as a nitrocellulose filter membrane. 

The third method does not detect the viral DNA or protein components but the antigens. In this immunoassay the antibodies are both localized on a biochip surface and on a SERS-active particle, which is in addition also marked with a SERS label. The antibodies can then either bind to the viral particles [37] or the isolated antigens [38]. For both variations the presence of viral particles or antigens leads to a SERS signal at the corresponding spot on the biochip. 

The idea behind a spintronic biochip or biosensor is to replace traditionally used fluorescent markers by magnetic labels. Instead of detecting biomolecular recognition using expensive optical or laser-based... 

A typical gene expression profiling experiment takes place in five separate processes. They are (i) microarray fabrication, (ii) purification and labeling of the target material, (iii) hybridization, (iv) detection and (v) data analysis. The characteristics of each step were briefly discussed in the introduction. A closer look at each of these steps is the object of this section. Here we mainly refer to biochips where the probe is constituted by nucleic acids (DNA microarrays). 

X. Gao, H. J. Mathieu, and M. Schawaller, Surface modification of polystyrene biochip for biotin labelled protein/StreptAvidin and NeutrAvidin coupling used in fluorescence assay,... 

Nanofilms and nanoclusters Energy sources driving fluorophores of biochip-bound labels. J. Nanosci. Nanotechnol 1(4) 397-405... 

Yeo WS, Min DH, Hsieh RW, Greene GL, Mrksich M. Label-free 76. detection of protein-protein interactions on biochips. Angew. 

Figure 11.4. A spotted DNA array with two-color detection of hybridization. An example of a spotted DNA array (16 X 20 elements) is shown after hybridization with two differentially labeled cDNA preparations, Cy3 (pseudo-colored green) and Cy5 (pseudo-colored red). The overlaying of the green and red images produces the image shown. The hue of each spot, ranging from green to red, indicates the relative expression level for the gene specific for each spot (image courtesy Packard Biochip Technologies). See color insert.

Moreover, an application on biochips for the determination of certain proteins in a serum has been presented. The attachment takes place, for instance, on an immobilized enzyme with the read-out of information normally being enabled by fluorescence labeling. Besides an external fluorescence label, it is also possible to employ the inherent luminescence of lattice defects in the diamond itself (Section... 

Abstract In this perspective article, we introduce a potentially transformative DNA/RNA detection technology that promises to replace DNA microarray and real-time PCR for field applications. It represents a new microfluidic technology that fully exploits the small spatial dimensions of a biochip and some new phenomena unique to the micro- and nanoscales. More specifically, it satisfies aU the requisites for portable on-field applications fast, small, sensitive, selective, robust, label- and reagent-free, economical to produce, and possibly PCR-free. We discuss the mechanisms behind the technology and introduce some preliminary designs, test results, and prototypes. 

S. Nock, Establishment of intein-mediated protein ligation under denaturing conditions C-terminal labeling of a single-chain antibody for biochip screening, Bioconjugate Chem. 2002, 13, 707-712. 

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