In this paper,we proposed a facile and accurate way for controlling multiplex fluorescent logic gates through changing the exciting and the observing wavelengths.As proof-of-principle,a Pb2+-specific DNAzyme probe and a thymine(T)-rich DNA probe were introduced to a double-stranded(ds-)DNA.The addition style of the two ions served as the four inputs by changing the distance of the three fluorophores,6-carboxyfluorescein(FAM),ALEXA 532(ALEXA)and carboxytetramethylrhodamine(TAMRA),all of which were modified on the dsDNA probe.Compared with the previous methods,the present approach needed neither different inputs nor the change of sequence of the probe to achieve multiplex logic gates.Furthermore,the modularity of the strategy may allow it to be extended to other types of logic gates.
TAO JiaZHENG JingLI JiShanZHAO PengLI JuanPingMA ChengYI MeiYANG RongHua
Two new anthryl-appended porphyrin dyads have been synthesized and used as highly selective and sensitive fluorescence probes for singlet oxygen ( 1O2 ). The design strategy for the probes is directed by the idea of intramolecular fluorescence resonance ener- gy transfer (FRET) interactions and carried out by incorporation of an electron-rich fluorophore (porphyrin) with a reactive anthracene for 1O2 . The molecular recognition is based on the specific interaction of 1O2 with the inner anthracene moiety, and the signal reporter for the recognition process is the porphyrin fluorescence. As a result of overlap of the emission band of the anthracene with the absorbance band of the porphyrin, intramolecular FRET occurs between the anthracene (donor) and the porphyrin (acceptor). The effective light absorbed by the porphyrin and, concomitantly, the emitted light intensity are thus modulated by the emission intensity of the anthracene. Upon reaction with reactive oxygen species such as hydrogen peroxide, hypochlorite, superoxide, hydroxyl radicals, and 1O2 , the probes exhibit a selective response toward 1O2 . In addition, significant amplification of the signal transducer is observed. The feasibility of the design was demonstrated by monitoring the 1O2 generated from a MoO42/H2O2 system. The results clearly demonstrate that the synthesized probes exhibit both high selectivity and high sensitivity for 1O2 . The fluorescence reaction and signal amplification mechanism of the system were both discussed, clearly confirming that the introduction of electron-rich porphyrin units into the 9,10-positions of anthracene can improve the response sensitivity and activate the probe's reactivity toward 1O2 .
A new biosensor platform was explored for detection of surfactant based on fluorescence changes from single strand DNA （ssDNA） and single-walled carbon nanotubes （SWNTs）. Thermodynamics assay was performed to value the stability of probe. The affinities of SWNT to five common surfactants （SDS, DBS, Triton X-100, Tween-20 and Tween-80） were investigated by real-time fluorescence method. The effects of Mg^2＋ and pH on the fluorescence intensity of self-assembled quenched sensor were performed. The fluorescent emission spectra were used to measure the responses of self-assembled quenched fluorescent of ssDNA/SWNTs to different concentration surfactant（Triton X-100）. The FAM-DNA wrapped SWNTs probe was stable in a wide temperature range （5 ℃ to 80℃）. The binding strength of surfactants and single-stranded DNA （ssDNA） on SWNTs surfaces was shown as follows： Triton X-100〉DBS〉Tween-20〉Tween-80〉ssDNA〉SDS, and the optimized reaction conditions included pH 7.4 and 10 mmol/L Mg2＋. The fluorescence of FAM-ssDNA wrapped SWNTs was proportionally recovered as a result of adding different concentrations of Triton X- 100, which realizes the quantitative detection of Triton X- 100.
