Hi everyone, I would like to start my first 2020 blog wishing you a successful year! This opportunity I thought to introduce a concept that is part of my current lab work and consists on a technological application at microscale known as Microarray.
Sometimes in a daily routine we don’t realize about the size or dimension of the things we use to do research. If we take a look at the biological microscale it might be interesting to see that antibodies, proteins, DNA and bacteria are found in the order of nanometers (nm or 10-9meters) to millimeters (mm or 10-3meters), probably units that are not familiar to everyone. Although we can’t distinguish them by naked eye, advances in molecular biology and technology make possible their manipulation at unimaginable scales.
In this context, microarrays emerge as technological tools at microscale, making use of nanobiomaterials in a wide range of applications. Microarrays can be defined as laboratory tools based on discrete immobilization patterns of molecules or fragments, in general DNA or proteins, over a supporting material (such as a glass or plastic slide) for use in biochemical or genetic analysis. This technology is relatively new in science; it was first described by Cook et al. (1997) and Felder and Kost (1998) for an Antibody microspot array, some authors consider the late 90’s and 2000’s as the birth of modern DNA arrays.
This laboratory tools are fabricated with high precision robotic printers that automatically deposit around 5000 molecules on a standard microscopic glass slide with a spot diameter between 80 and 200 micrometers or are synthesized by the process of photolithography. The distance between spots is less than 1.5mm and a maximum spot size less than 1.0mm. As an example, a useful range of spots delivery volumes is 250pL (picoliters) to 100nL (nanoliters), to generate symmetric spheres.
This molecular receptor arrays allows the simultaneous detection of a large number of substances in a reduce space with significantly low volumes of samples. This aspect is interesting while making high throughput analysis, like for example genetic studies, expression profiles and so on.
Nowadays plenty of different applications have been derived from the basic principle behind this technology at microscale. On one hand DNA microarrays evolve as screening tools to study thousands of genes, comparing profiles of expression over different conditions at the same time1. In general, DNA arrays are used to probe a solution of a mixture of labeled nucleic acids and the binding (by hybridization) of these “targets” to the “probes” on the array is used to measure the relative concentrations of the nucleic acid species in solution. By generalizing to a very large number of spots of DNA, an array can be used to quantify an arbitrarily large number of different nucleic acid sequences in solution.2
On the other hand protein microarrays immobilize enzymes and antibodies over supporting elements and play an integral role in biomolecular detection for diagnostic, competing with well established methods like ELISA. In general, most of immunoassay can be transferred into microarray format acquiring numerous advantages like multiple analyte sample processing and reducing the time of assay.
Following the same principles but in a considerable lower space, proteomic microarrays require capture and detection molecules with high affinities and low dissociation rates so protein detection will be seen over a reasonable concentration range for the experiment. These analytical devices have exhibited explosive growth over the past years and current advances in nanotechnology and robotics allow new developments and applications. Microarrays of immobilized functional proteins have the potential to increase dramatically the throughput of proteomic analysis3.
For several reasons DNA microarrays were developed before protein microarrays. DNA molecules are much more robust and easy to handle than proteins. Nucleic acids are physically and chemically similar allowing standardization of manufacturing and assay procedures; DNA hybridization reaction exploited in DNA microarrays is simple and depends only on nucleotide sequence. On the contrary, protein binding depends on primary sequence, and tertiary structure, even homologous proteins with a different amino acid or posttranslational modification can present significant differences in their stability or folding structure.
Microarrays can be used in a large number of applications considering high-throughput as the major goal. This technology involve a wide range of research fields such as microfabrication and micromechanics, chemistry, enzymology, microfluidics, genomic, optics and bioinformatics. That’s why this versatile and promising technology is still offering plenty of applications.
1 Amaratunga, D., Göhlmann, H. & Peeters, P. Microarrays. (2007).
2 Bumgarner, R. Overview of DNA microarrays: types, applications, and their future. Current protocols in molecular biology 101, 22.21. 21-22.21. 11 (2013).
3 Wilson, D. S. & Nock, S. Functional protein microarrays. Current opinion in chemical biology 6, 81-85 (2002).