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We herein constructed a sensor that converts target DNA hybridization-induced conformational transformation of the probe DNA to electrochemical response based on host-guest recognition and nanoparticle label. In the sensor, the hairpin DNA terminal-labeled with 4-((4-(dimethylamino)phenyl)azo)benzoic acid (dabcyl) and NH2 group was immobilized on multi-walled carbon nanotube modified glassy carbon electrode (MCNTs/GCE) surface, and the Au nanoparticles surface-modified with b-cyclodextrins (CD-AuNPs) were employed as electrochemical signal provider and host-guest recognition element. Initially, the probe DNA immobilized on electrode kept the stem-loop configuration, which shielded dabcyl from docking with the CD-AuNPs in solution due to the steric effect. After target hybridization, the probe DNA underwent a significant conformational change, which forced dabcyl away from the electrode. As a result, formerly-shielded dabcyl became accessible to host-guest recognition between b-cyclodextrin (b-CD) and dabcyl, thus the target hybridization event could be sensitively transduced to electrochemical signal provided by CD-AuNPs. This host-guest recognition-based electrochemical sensor has been able to detect as low as picomolar DNA target with excellent differentiation ability for even single mismatch.

This communication reports on a new electrochemical method to detect the hybridization specificity in homogenous solution by using host-guest recognition technique. A hairpin DNA with a dabcyl molecule which is typical guest molecule to b-CD at the 3’-terminus and a NH2 linked at the 5’-terminus as the probe DNA. The probe DNA was immobilized on the PdS nanoparticle to construct a double-labeled probe (DLP) and could selectively hybridize with its target DNA in homogenous solution. A b-CD modified Poly(N-acetylaniline) glassy carbon electrode was used for capturing dabcyl in DLP. Without binding with target DNA, the DLP keep stem-loop structure and block dabcyl enter into the cavity of b-CD on electrode. However, a target-binding DLP is incorporated into double stranded DNA, causing loop-stem structure opened and dabcyl could be easy captured by b-CD which brought DLP on electrode surface. With electrochemical measurement, the signal come from Pd2+ be used for target DNA quantitative analysis.

In this paper, a novel dually-labeled DNA probe (DLP) in a stemloop structure was designed to be labeled at one end with dabcyl, working as a guest molecule, and at its another end with CdS nanoparticle, working as an electrochemical tag to indicate the electrochemical signal of hybridization occurrence. One a-cyclodextrin/multi-walled carbon nanotube modified glassy carbon electrode (a-CD/MCNTs/GCE) was fabricated for the hybridizer capture. The DLP could recognize target DNA through hybridization event between complementary bases in the loop of probe DNA and target DNA. Without binding with target DNA, the DLP kept its stemloop structure which held dabcyl molecule shielded by the loop of probe DNA and CdS nanoparticle. This structure blocked dabcyl from entering the cavity of a-CD on the electrode. Once hybridization happened, the stem-loop structure of hairpin DNA opened and then dabcyl molecule could be easily captured by a-CD on the electrode. Thus, the electrochemical response of the CdS nanoparticle label at the other end of the hybridizer was proportional with the concentration of target DNA.