Fluorogens with aggregation-induced emission (AIEgens) are a unique type of luminescent materials for sensing and imaging applications. The integration of AIE characteristics into metal–organic frameworks (MOFs) structure is an emerging research field that has greatly advanced the optical properties of MOFs. This Review mainly focuses on the development of AIE MOFs with highlights on materials development and their applications in analytical and biomedical fields. The first part discusses the structure design for AIE MOF from the perspective of linkers, metal nodes, and heterogeneous composites. The second part summarizes the major mechanisms on the property modulation of AIE MOFs in response to different stimuli based on fluorescence quenching, in-situ restriction of intramolecular motion, and framework deformation switches. The outlook elaborates on the potential of AIE MOFs, which have opened a new dimension in luminescent material development.

A DNA walker as a new molecular machine can walk on defined tracks to directly generate signal indicators in biosensing and biomedical applications. In this work, a tandem signal amplification strategy was developed on the basis of the DNA-walker-induced conformation switch for bridging palladium nanoparticles/metal−organic framework tags in ultrasensitive electrochemical DNA biosensing. The signal tags were synthesized by in situ reduction of Pd nanocrystals on porphyrinic metal− organic frameworks (PCN-224), followed by conjugation with streptavidin (SA). The as-prepared Pd/PCN-224-SA tag could electrocatalyze the oxidation of NaBH 4 with high efficiency for signal readout. The presence of target DNA released swing arms that were each silenced by a blocker, and then the activated swing arms could hybridize with hairpin DNA. The movement of swing arms was powered by enzymatic cleavage of conjugated oligonucleotides, inducing the allosteric switch from hairpin to SA aptamer. Therefore, Pd/PCN-224-SA tags were brought onto the electrode surface via SA-aptamer biorecognition to generate the enhanced electrochemical signal. The DNA walker-based electrochemical biosensor demonstrated good performance such as 6 orders of magnitude linear range, femtomolar detection limit, and single mismatch differentiation ability. Moreover, the feasibility of the biosensor was identified in serum matrixes. The tandem signal amplification of metal−organic frameworks and DNA walkers provided a new avenue in trace electrochemical biosensing.

Different from conventional DNA walkers, we designed a telomerase-triggered three-dimensional DNA walker consisting of a superhairpin structure with a bulged loop in the stem as the walking strand and dye-labeled tracks for ultrasensitive detection of telomerase activity. In the presence of telomerase, the primers in the stem of the superhairpin structure were elongated and triggered internal strand displacement, thus activating the superhairpin structure. Subsequently, the open superhairpin structure as a swing arm was able to bind with the track, and the swing arm could be released by enzymatic cleavage of the binding duplex domain, resulting in the fluorescence recovery of dye-labeled fragments from the surface of gold nanoparticles. Based on signal amplification of the telomerase-triggered DNA walker, the walking device was further applied to various cancer lines with a low detection limit of telomerase activity equivalent to 90 cells μL −1 for HeLa cells. Moreover, the advantage of this DNA walker strategy was confirmed by calculating telomerase activity in a single cell. This telomerase-triggered DNA walker provides a new concept on signal transduction for telomerase detection and is anticipated to stimulate interest in DNA nanomachine design for bioanalysis.

No abstract

Tetrapod DNA quadruplexes were designed for assembly and precise modulation of light emission of an oligonucleotide-grafted fluorogen with aggregation-induced emission.