Aptamers negative selections

Negative selections have not proven to be necessary in CE-SELEX selections. No aptamers have been identified that exhibit affinity for the capillary surface. This has been equally true for selections performed using uncoated or neutrally coated capillaries. This greatly simplifies the SELEX procedure and removes one of the significant pitfalls of aptamer selection. 

While indirect selections work quite well for antibodies they have been less successful in the case of catalytic nucleic acids. There are only three examples which prove that it is possible in principle to obtain a ribo- or deoxyribozyme by selecting an aptamer that binds to a TSA A rotamase ribozyme [7], a ribozyme capable of catalyzing the metallation of a porphyrin derivative [92], and one catalytic DNA of the same function [93]. Another study reported the selection of a population of RNA-aptamers which bind to a TSA for a Diels-Alder reaction but the subsequent screen for catalytic activity was negative for all individual RNAs tested [94]. The attempt to isolate a transesterase ribozyme using the indirect approach also failed [95]. 

Automated SELEX is just one example of the many modified SELEX procedures developed to improve aptamer selection. Other screening technologies have been developed to improve the selectivity of an aptamer, such as subtractive SELEX, negative SELEX, counter SELEX, and photo SELEX to create a more universal aptamer selection process with complex target SELEX, blended SELEX, and toggle SELEX and to improve the efficiency of obtaining aptamers such as non-SELEX and capillary electrophoresis (CE) SELEX. ... 

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