| Water-soluble fluorescent conjugated polythiophenes, featured π-delocalized electronic structures, have attracted increasing attention as novel functional materials and have been successfully employed as label-free optical probes in biosensing applications in recent years.In this paper, we designed and synthesized three types of water-soluble polythiophene derivatives:poly(3-(1’-ethoxy-2’-N-methyl imidazole)thiophene) (PT1), poly(3-methyl-4-(1’-ethoxy-2’-N-methyl imidazole)thiophene) (PT2) and binary copolymer (CoPT). Their molecular structures were charactered by FT-IR,’H-NMR,13C-NMR, UV-Vis and PL.Photophysical properties of monomer1, monomer2, PT1, PT2 and CoPT were measured by UV-Vis absorption spectrum and fluorescence spectrum. The results showed that the maximum absorption wavelengths(λmax) of monomerl and monomer2 are located at 236nm and 234nm, respectively, and the maximum fluorescence emission wavelengths (λem) are located at 367nm and 361nm, respectively. The solution can emit bright bule light. While the λmax and λem of PT1, PT2 and CoPT are appeared at 506nm,370nm,452nm and 544nm, 526nm,504nm, respectively. The PT1 and CoPT can emit bright yellow light and the PT2 can emit bright green yellow light. The relative fluorescence quantum yield of three polythiophene derivatives were determined by "suction point excitation fluorescence correction integral area method and the measured value were 0.33%,0.19% and 0.35%, respectively.The temperature-responsive, solvent-responsive and pH-responsive of PT1, PT2 and CoPT were investigated by UV-Vis absorption spectrum, the results showed that:1) With increasing of solution temperature, the λmax of PT1, PT2 and CoPT were bule shifted from 519nm to 515nm, from 371 nm to 365nm and from 447nm to 430nm, respectively; 2) In pure water, water/methanol, water/ethanol and water/acetonitrile, with the decrease of solvent polarity, the λmax of PT1, PT2 and CoPT were red shifted from 512nm to 520nm, from 366nm to 373nm and from 434nm to 446nm, respectively; 3) With the reduction of pH in the range of 4 to 9, the λmax of PT1, PT2 and CoPT were red shifted from 522nm to 530nm, from 367nm to 381nm and from 459nm to 470nm, respectively.The performance of PT1, PT2 and CoPT on Tβ4 was studied, the results indicated that:1) The fluorescence intensity of PT1, PT2 and CoPT decreased significantly while adding ss-DNA (Tβ41), and the maximum fluorescence quenching rate would reach 33.3%,25.4% and 28.6%, respectively. The fluorescence intensity ration (I0/I), in a certain range, increased gradually with a red shift in the emission spectrum while the concentration of Tβ41 increased, and the λem of PT1, PT2 and CoPT were red shifted from 544nm to 552nm, from 500nm to 507nm and from 538nm to 544nm, respectively. Upon adding the Tβ41’, the two complementary ss-DNA would hybridize and the PTs were thus released and then twined around the double helix due to electronic attraction, forming a triplex system and regained its fluorescence emission properties. With the successive addition of Tβ41 and Tβ41’, the color of PT1 and CoPT changed from light yellow to dark yellow and then back to bright yellow, while the color of PT2 changed from light green yellow to dark green yellow and then back to bright green yellow; 2) In the low concentration ranging from 1.3×10-9M to 1.3 × 10-10M, the I0/I was linearly dependent on the concentration of Tβ41, which conforms to the Stern-Volmer equation, the related fitting equations were I0/I=1.03+0.15C (R2=0.99),I0/I=0.96+0.15C (R2=0.99) and I0/I=0.96+0.14C (R2=0.99), respectively, the Stern-Volmer constant (Ksv) were 0.15×109M-1, 0.15×109M-1 and 0.14×109M-1, respectively, and the minimum detection limit of PT1, PT2 and CoPT would reach 1.3×10-10M,4.0×10-10M and 4.0×10-10M, respectively.The performance of PT1, PT2 and CoPT on BRCA was studied, the results indicated that: 1) The maximum fluorescence quenching rate would reach 60.1%,23.5% and 28.6% while adding ss-DNA (BRCA1), respectively. The fluorescence intensity ration (I0/I), in a certain range, increased gradually with a red shift in the emission spectrum while the concentration of BRCA1 increased, the λem of PT1, PT2 and CoPT were red shifted from 540nm to 547nm, from 502nm to 512nm and from 538nm to 547nm, respectively. The fluorescence intensity of polythiopheners could recover to its initial intensity when complementary BRCA1’was added, and with the successive addition of BRCA1 and BRCAl’, the color of PT1 and CoPT changed from light yellow to dark yellow and then back to bright yellow, while the color of PT2 changed from light green yellow to dark green yellow and then back to bright green yellow; 2) In the low concentration ranging from 1.3×10-9M to 1.3×10-10M, the I0/I was linearly dependent on the concentration of BRCA1, the related fitting equations were I0/I=-0.48+0.40C (R2=0.99),I0/I=0.94+0.10C (R2=0.98) and I0/I=1.02+0.13C (R2=0.99), respectively, the Ksv were 0.40×109M-1,0.10×109M-1 and 0.13×109M-1, respectively, the minimum detection limit of PT1, PT2 and CoPT would reach 5.3×109M-1,8.0×10-10M and 1.3 ×10-10M, respectively. Among them, the sensitivity of PT1 is up to 0.40 × 109 M-1 which is about 4-fold higher than that of PT2 and CoPT. Meanwhile, the sensitivity of PT1 for detecting BRCA1 is nearly 3 times higher than that for Tβ4. As a result, water-solution cationic poly(3-(1’-ethoxy-2’-N-methyl imidazole)thiophene) (PT1) might be more suitable for detecting BRCA DNA.For Tβ4, the measured LOD values of PT 1, PT 2 and CPT were 0.06nM,0.06nM and 0.06nM, respectively and the measured LOQ values were 0.12nM,0.20nM and 0.12nM, respectively; For BRCA1, the measured LOD values of PT 1, PT 2 and CPT were 0.02nM, 0.09nM and 0.07nM, respectively and the measured LOQ values were 0.07nM,0.29nM and 0.12nM, respectively. |
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