Biochips – fundamentals and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 331

analysis of low abundant proteins. As a result, they cannot meet the requirements of
automation and high throughput analysis. Protein biochips or protein microarrays are an
emerging alternative technology to increase the overall throughput at reduced cost. By
providing an addressable array of spots, with analytes detected by methods such as mass
spectrometry or fl uorescence, protein chips eliminate much of the irreproducibility and
complexity of 2D-gel analysis.

11.3.2 Fabrication of protein chips
11.3.2.1 Types of protein chips
Currently, protein microarrays can be divided into various types depending on the
strategies to be chosen. For example, according to the array structure and shape, pro-
tein microarrays include 3D-surface structure [30, 31], nanowell [32], and plain chips
[33-36]. Meanwhile, considering the fi eld of application, protein microarrays can be
classifi ed into fi ve categories: antibody array, antigen or reserve array, functional array,
capture array, and solute array. Table 11.6 shows the differences among them.
The principle of antibody arrays, and their converse counterparts, antigen or reverse
arrays, is to use high affi nity ligands to detect the presence of specifi c proteins and
biomarkers in a complex mixture. Knezevic et al. [38] selected 368 antibodies spe-
cifi c to cancer-related proteins. Exposure of the printed arrays to six categories of his-
tologic lysates identifi ed 11 proteins that showed consistent change in expression or
state of phosphorylation. Sreekumar et al. [39] used an array of 146 distinct antibodies
to monitor alterations of protein levels in colon carcinoma cells. Paweletz et al. [40]
used this technique to reproducibly quantify the status of signal proteins in 3 nL spots
containing whole protein repertoires of lysed cell proteins, and peptides and nucleic

TABLE 11.6
Types of protein microarrays [37]

Array type Description

Antibody array Polyclonal or monoclonal antibodies are arrayed and used to detect and

quantify specifi c proteins in a biological sample. An antibody array is

effectively a parallel series of miniature immunoassays

Antigen or reverse array The converse of an antibody array, this chip has immobilized antigens that are

used to detect and quantify antibodies in a biological sample

Functional array Purifi ed proteins are arrayed on the surface and used to detect and characterize

protein - protein, protein - DNA or protein - small molecule interactions

Capture array Non-protein molecules that interact with proteins are immobilized on the

surface. These may be broad capture agents based on surface chemistries such

as the Ciphergen Protein Chip, or may be highly specifi c such as molecular

imprinted polymers or oligonucleotide aptamers

Solute array The potential next generation of arrays is to have nanowells containing coded

microspheres or barcoded nanoparticles in solution