Natural and artificial ribozymes can catalyse a diverse range of chemical reactions. Through recent efforts in enzyme engineering,

it has become possible to tailor the activity of ribozymes to respond allosterically to specific effector compounds. These allosteric

ribozymes function as effector-dependent molecular switches that could find application as novel genetic-control elements,

biosensor components or precision switches for use in nanotechnology.

It is possible to find RNA sequences that can selectively bind to a given target (aptamers) using techniques such as SELEX. The sensing of small molecules by these aptamers can be transduced to give an observable output. These sensor modules can then be combined with ribozymes to achieve ligand dependent activity. This has applications in control and sensing of gene expression. Two representative publications are given below.

Another class of nucleic acid switches is that of transcription based genetic networks. It has been shown that these nucleic acid switches can be used to perform various types of computation. Exciting applications exist in the field of Synthetic Biology. A few publications are given below. 

Another class of nucleic acid switches change conformation based on the local environment such as pH, presence of ligands etc. An example of the same is the i-motif, a DNA sequence that folds under a low pH. These switches can then be used as sensors to report on the cellular environment. 

A few researchers that I know of in this area are - Dr. Christina Smolke, Dr. Yaakov Benenson, Dr. Yamuna Krishnan, Dr. James Collins

As the term is broad, it can be interpreted in multiple ways some of which are given above. 

https://med.stanford.edu/profiles/christina-smolke?tab=bio

http://www.silva.bsse.ethz.ch/synbio/research/index

https://chemistry.uchicago.edu/faculty/faculty/person/member/yamuna-krishnan.html

http://collinslab.mit.edu/

Article A modular and extensible RNA-based gene-regulatory platform ...

Article The i-motif in nucleic acids

Article Construction of a Genetic Toggle Switch in Escherichia coli

Article In Vitro Selection of RNA Molecules that Bind Specific Ligands

Article Versatile RNA-sensing transcriptional regulators for enginee...

Article Biomolecular computing systems: Principles, progress and potential

Article Two DNA nano machines map pH changes along intersecting endo...