4.11. Microarrays

A microarray is a powerful multiplex detection technology consisting of an ordered array of hundreds of molecular probes specific for different target RNAs bound to a solid support, usually a slide. The target sequences in an RNA sample are hybridized to these probes and these hybridization events are detected by a variety of, usually optical, detection chemistries (de Miranda, 2008). The power of the technology lies in the massive multiplexing potential where the relative and absolute amounts of hundreds of different targets can be determined simultaneously (Cheadle et al., 2003; Gentry et al., 2006). As molecular biology, pathology and diagnostics moves away from single organism/gene effects to surveying interactions among pathogens and (host) genes, microarray-based diagnostics will become increasingly relevant. Microarray printing technology is becoming cheaper and more reliable, and single-use disposable microarrays for specific multi-target diagnosis are increasingly available (Yuen et al., 2003; Lieberfarb et al., 2003; Noerholm et al., 2004; Lin et al., 2004; Perreten et al., 2005; Fiorini et al., 2005). Uniformity of hybridisation across the microarray, important for reliability in quantitation, is maximized with a range of nano-technological innovations (Yuen et al., 2003; Noerholm et al., 2004; Fiorini and Chiu, 2005), improved oligonucleotide design (Rouillard et al., 2003) and with replication of the spots or even whole arrays (an array of arrays) across the slide. The probe-target hybridisation can be detected through FRET-based probes, SYBR-green-I dye, or labelling of the nucleic acid sample containing the target sequences. Microarray technology can also be combined with quantitative RT-PCR, multiplex (pyro)sequencing and label-free electronic or optical detection technologies to increase the speed, accuracy, specificity or information content of the diagnosis (Weidenhammer et al., 2002; Erali et al., 2003; Gharizadeh et al., 2003; Fixe et al., 2004).

Numerous honey bee arrays have already been designed for different research purposes (Whitfield et al., 2002; Evans and Wheeler, 2000; 2001; Robinson et al., 2006). A microarray has also been developed for the semi-quantitative detection of honey bee viruses (Table 5 in Glover et al., 2011) which will be developed further for diagnostic purposes.

Microarrays can also be developed for serology-based detection of proteins (Sage, 2004), using a similar approach as the sandwich ELISA (Enzyme-Linked ImmunoSorbent Assay: see de Miranda et al., 2013). The probe-target recognition events are visualized and detected using similar detection chemistries as for nucleic acid-based microarrays.