Coralyne is a crescent-shaped planar heterocyclic molecule that is capable of binding to duplex and triplex DNA. As a synthetic derivative of protoberberine alkaloids, coralyne exhibits powerful anticancer activity against P388 and L1210 leukemias in animal models such as mice. The potential medicinal impact of coralyne in cancer therapeutics is particularly attractive because of its relatively low toxicity, which has led to the deep investigation of its molecular interactions with nucleic acids and the synthetic development of various coralyne derivatives. One of the most important chemical and biological properties of coralyne is its molecular recognition of specific nucleic acids, or polyadenine (poly-A), with a strong binding affinity (binding constant = 1.8 × 10 M) and a stoichiometry of one coralyne to four adenine bases. In fact, most mRNA sequences contain a number of poly-A residues at their 3' end, which is essential for determining the mRNA stability and maturation, and for initiation of translation. Considering that the drug design associated with gene regulation typically requires specific binding to unique structural regions in mRNA such as poly-A, the chemical, biological, and physiological applications of coralyne still essentially require further vast investigation. Based upon such importance, there have been a few reports for the detection of coralyne in aqueous media using unmodified DNA sequences, fluorophores, unmodified silver nanoparticles, and unmodified or DNA-modified gold nanoparticles. These methods are in common based upon the non Watson-Crick base pair interactions of adenineadenine (A-A), where coralyne (CR) strongly intercalates the poly-A/poly-A duplex via A-CR-A chemistry. 3-5 While sensitive, however, they often suffer from costly instrumentation for photoluminescence, employ a temperature controller, and most of all, exhibit limited or unconfirmed selectivity. Therefore, the development of a selective and sensitive assay to detect coralyne is highly demanded. In this Note, we present a new colorimetric assay to detect coralyne based upon the kinetic observation of the DNAfunctionalized gold nanoparticles (DNA-AuNPs) and their hybridization in the presence of coralyne. We have taken advantage of (1) the difference in kinetics of DNA-AuNPs' hybridization determined by their DNA loading, (2) the distance-dependent optical properties of DNA-AuNPs based upon surface plasmon resonance (SPR), and (3) the specific A-CR-A intercalation chemistry. This assay is conducted at room temperature and does not require any expensive instrumentation. Importantly, we have hypothesized that the DNA-AuNP hybridization kinetics is dramatically enhanced in the presence of coralyne than the other DNA-binding molecules, which would lead to a target-specific visible response of the system to coralyne. The assay began by combining the DNA-AuNP probes (DNA 1 and DNA 2) with various DNA-binding molecules (Scheme 1) at room temperature, and monitoring their extinction at 525 nm as a function of time ([DNA 1] = [DNA 2] = 0.5 nM, [DNA-binding molecule] = 5 μM). In the absence of a DNA-binding molecule (Blank), the DNAAuNPs assembled to form aggregates slowly via WatsonCrick base pairing with a decrease in extinction at 525 nm. On the other hand, however, coralyne dramatically accelerated the macroscopic aggregate formation of the DNAAuNPs with a concomitant color change from red to purple, indicating that the DNA-DNA hybridization took place via A-CR-A intercalation chemistry in a kinetically favorable manner (Fig. 1(a)). To systematically evaluate the selective binding of coralyne for A-A mismatches, we prepared eight identical batches of the DNA-AuNP probe solutions and combined each of them with pure water (Blank), coralyne (CR), and structurally compatible and physiologically relevant other intercalators such as ethidium bromide (EB), neomycin (NM), 4,6-diamidino-2-phenylindole (DAPI), 9aminoacridine (AA), palmatine (PT), and berberine (BR), respectively. After 15 minutes, only the mixture containing