**Acknowledgements**

We would like to thank Lakshmi Narayanan Gopalan for his assistance in the preparation of figures. The salary support for this work was provided by Indo-Finland research grant (IV4SP-FinSynBio-Synthetic Biology), funded by Department of Biotechnology, Government of India (Grant number BT/IN/ Finland/29/MN/2013).

*Role of Novel Drug Delivery Vehicles in Nanobiomedicine*

tating high-throughput selection of aptamers.

high-affinity Ang2 aptamers with Kd <30 nM.

just one round of positive selection followed by HTS [96].

stages and only individual stages in a pipeline are partially automated, independent of each other [86]. The advantage of unit-automation is that it keeps a highly open architecture of the pipeline allowing individual modules to be easily modified or

Unlike the discovery of small molecule-based drugs in industry, where automation is a norm, development of novel aptamers has happened in individual labs in an academic research setting. For truly industrializing the aptamer discovery process, it is imperative to develop high-throughput strategies for aptamer development at different levels, *viz.*, aptamer selection process, sequencing, and characterization of aptamers involving affinity and specificity studies toward its target. Here we discuss about the high-throughput technologies which have been developed facili-

The first attempt to automate aptamer selection process was performed by the group of Ellington [82] followed by some other improvements [88–92]. It brought down the selection time from weeks or months to days. Automation of the SELEX process increased the throughput of selections, but shifted the bottleneck within a

In 2011 the group of T.M. Soh developed a Quantitative Parallel Aptamer Selection System (QPASS), which integrates microfluidic aptamer selection (M-SELEX) and next-generation sequencing (NGS) with in situ synthesized aptamer arrays, enabling simultaneous measurement of affinity and specificity of several 1000 candidate aptamers in parallel. Major advantage of this high-throughput platform is that it automated the characterization, i.e., finding the affinity and specificity of aptamers which is a major bottleneck in aptamer selection, since traditionally the affinity and specificity of aptamers is measured individually in a serial manner [93]. This group used angiopoietin-2 (Ang2) as a target and performed four rounds of M-SELEX followed by next-generation sequencing to obtain enriched aptamer sequences. Next, using aptamer arrays they simultaneously measured dissociation constant (*Kd*) of ∼1000 aptamer candidates in parallel, identifying six

Development of NGS platform in the last decade has revolutionized the aptamer

Since the inception of aptamer technology, this field has significantly evolved

with its foray into a wide variety of applications, including targeted delivery. Aptamers caught the attention of researchers due to their unique advantages for use in therapeutics in nanomedicine due to their small size that gives higher penetration in tissues as compared to antibodies, ease of synthesis, high specificity and affinity that is comparable with antibodies and ease of chemical modifications that allowed

selection process. The Schroeder group in 2010 made the initial attempt in this direction as they combined genomic SELEX with high-throughput sequencing for the identification of genomic aptamers [94]. The same year, Soh group (2010) integrated microfluidic SELEX with high-throughput sequencing to obtain novel aptamers against platelet-derived growth factor BB (PDGF-BB) protein in just three rounds of selection, which traditionally takes 12–20 rounds [95]. Advantage of HTS is that it can track the copy number and enrichment fold of more than 10 million individual aptamer sequences through multiple rounds of selection. This enables the identification of high-affinity aptamers without the need of fully converging the aptamer pool to a small number of sequences, which is required for cloningbased selection method. Similarly, Hoon et al. obtained high-affinity aptamers after

exchanged; hence, the pipeline can be easily extended or modified [87].

selection pipeline toward the identification and evaluation side.

**14**

**10. Conclusion**
