Colorimetric enantiorecognition of oligopeptide and logic gate construction based on DNA aptamer-ligand-gold nanoparticle interactions.

Enantiomers of chiral biomolecules and drugs have distinct pharmacological and toxicological activities. . Consequently, separation and determination of enantiomers are vital in pharmaceutical and chemical industries. It is wellknown that the l-enantiomer of oligopeptides naturally exists in the organism; however, d-oligopeptides are regarded as potential therapeutic agents because of their resistance to protease degradation. Thus, chiral discrimination of oligo ACHTUNGTRENNUNGpeptides has been a research focus, and will be required prospectively. In recent years, many methods based on fluorescence, UV/Vis and electrochemistry have been constructed for chiral recognition of biomolecules. However, colorimetric enantiorecognition of oligopeptides has not been reported. Herein, we have utilized unmodified gold nanoparticles (GNPs) as indicator and DNA aptamer as chiral selector, and have realized colorimetric and enantioselective recognition of one oligopeptide, arginine vasopressin (AVP). In addition, because of their convenient visual ACHTUNGTRENNUNGiza ACHTUNGTRENNUNGtion, colorimetric molecular logic gates have attracted researchers attention and they have been constructed for bio ACHTUNGTRENNUNGsensors, drug release, and self-powered biofuel cells. Therefore, we constructed two kinds of colorimetric logic gates (OR and INHIBIT) in combination with colorimetric enantiorecognition of AVP. AVP is a nine-amino acid cyclic hormone peptide, that exists in most mammals including humans, and acts as a modulator of neuronal function in the brain and regulates water absorption and urine production in the kidneys. Its primary structure is Cys-Tyr-Phe-Gln-Asn-Cys-ProArg-Gly-NH2, and has a disulfide bridge between Cys 1 and Cys residues. The disulfide group can adsorb onto gold surfaces. It is speculated that AVP can induce aggregation of citrate-coated GNPs, due to its two main functional groups, disulfide and guanidinium groups derived from cystine and arginine residues. Aptamers are selected in vitro by systematic evolution of ligands by exponential enrichment (SELEX), and are singlestranded DNA or RNA molecules that can bind various target ligands (i.e. , small-molecule drugs, peptides, proteins and cells) with high affinity and specificity. Analogous to cyclodextrins and their derivatives, macrocyclic antibiotics, and so on, varieties of aptamers have been exploited and utilized as chiral selectors for chiral separation and detection of target ligands. Williams et al. selected a nucleic acid aptamer that binds the d-enantiomer of AVP (dAVP). In this study, the d-enantiomer-specific aptamer (V-apt) was utilized as masking agent to impede GNP aggregation via binding interactions between d-AVP and Vapt, and as chiral selector to discriminate enantiomers of AVP. The sequence of V-apt is 5’-TCACG TGCAT GATAG ACGGC GAAGC CGTCG AGTTG CTGTG TGCCG ATGCA CGTGA-3’. Based on the interactions among DNA aptamer, oligopeptide ligand and gold nanoparticle, chiral recognition of AVP was realized (Scheme 1 and Scheme S1 in the Supporting Information).