DNA-regulated upconverting nanoparticle signal transducers for multivalued logic operation.

Molecular computing has attracted intense attention as an alternative to the traditional semiconductor silicon-based computing over the past decades. [ 1 ] Logic gates that integrate and convert input signals into a defi ned output, is the fundamental basis of computing. [ 2 ] So far, considerable research efforts have been dedicated to chemical and biological systems that are capable of mimicking logic operations on the molecular level. [ 3,4 ] Various materials including organic molecules, [ 5,6 ] biomolecules, [ 7–13 ] and polymers [ 14,15 ] were employed to construct Boolean logic gates, in which every bit is coded by 0 or 1, corresponding to a low or high signal, respectively. However, quite often, the complexity of information processing makes it diffi cult to identify certain and accurate signals based on low/high system. Multi-valued logic, compared to binary logic, shows great promise for dealing with uncertain information. It involves the switching between more than two states. This kind of system, which identifi es signal states more accurately and certainly, is important for the further development of molecular devices, but limited studies were developed. Ali et al. developed a multi-valued logic using a nanofl uidic diode based on conical nanopores functionalized with polyprotic acid chains. [ 16 ] Ferreira et al . designed a bifl uorohporic dyad to yield output with three signal levels. [ 17 ] Very recently, the ensemble of DNA on the surface of silica nanoparticles was designed to perform three valued logic. [ 18 ] Although promising, development of systems which could operate multi-valued logic still remains a big challenge. Upconversion nanoparticles (UCNPs), as novel luminescent nanomaterials with many distinctive physical and optical properties, have recently attracted extensive research interests. [ 19,20 ] Particularly, compared with down-conversion fl uorescent materials, up-conversion materials show very low background light and strong penetration abilities. [ 21–24 ] With the advantage of high chemical stability, no photobleaching, no blinking, and low toxicity, UCNPs are widely used for photoluminescence imaging, drug delivery and biomolecular sensing etc. [ 25–27 ] Moreover, barcode-based imaging or sensing which take advantage of multiple emissions of UCNPs have been achieved. [ 28–30 ] However, the UCNPs based logic systems have not been reported up to now. To explore the new dimensions of this interesting research area, we combine the inherent and unique characters of UCNPs with the application of DNA to regulate the emission of UCNPs and subsequently construct multi-valued logic. In this work, for the fi rst time, we reported the implementation of a UCNPs-based multivalued logic system including a ternary OR gate and an INH gate with nucleic acids applied. As shown in Figure 1 , DNA strand A was immobilized on the surface of the UCNPs which were well dispersed in solution. Upon addition of graphene, due to the π–π stacking effect between single strand DNA and the graphene sheet, the UCNPs were easily absorbed on the graphene sheet and the upconversion (UC) emission was quenched via Fluorescent resonant energy transfer (FRET). [ 31 ] DNA strand B containing 23 bases was designed to form a duplex of 18 base pairs with strand A. After formation of doublestranded DNA (dsDNA), the UCNPs were removed from the graphene sheet owing to conformation change of DNA and the UC fl uorescence could be recovered. DNA strand C with 28 bases was then added to initiate a displacement reaction of duplex AB. Strand B disassociated and duplex AC formed. As the strand C was modifi ed on fl uorescent silica nanoparticles (FLSiNPs), the formation of duplex AC brought UCNPs and FLSiNPs into close proximity. UCNPs exhibited two emission peaks at 550 nm (green emission) and 650 nm (red emission), respectively. The overlap between the absorbance band of FLSiNPs and the fi rst emission of UCNPs allowed for the FRET from UCNPs to FLSiNPs. The decrease of the fi rst emission of UCNPs could be observed. Meanwhile, the second emission of UCNPs overlapped with the emission of FLSiNPs, yielding increased red emission due to accumulation of the two signals. Based on above observation, we integrated the hybridization of DNA and the multiple emissions of UCNPs to construct ternary logic gates. By observing the change of fl uorescence intensity of UCNPs, the multi-valued logic could be operated. In the experiments, the amino-decorated water-soluble NaYF 4 :Yb,Er UCNPs (UCNP-NH 2 ) were synthesized by a solvothermal method reported previously. [ 32 ] Then surface of UCNPs-NH 2 were fi rstly modifi ed by the carboxylic group DOI: 10.1002/smll.201303138 Nanoparticles