Abstract: A method for preparing a dual-functional hybrid thin-film for self-calibration detection of tumor-derived exosomes is disclosed. A dual-functional hybrid thin-film, aptamer-BPNSs/Fc/ZIF-67/ITO, is constructed by facile self-assembly of a cobalt-based metal-organic framework (ZIF-67) composite doped with black phosphorus nanosheets (BPNSs), an aptamer and ferrocene (Fc) on an indium tin oxide (ITO) electrode. Methylene blue (MB) labeled aptamer specifically binds to CD63 protein to precisely capture protein. The protein is a specific biomolecule carried by breast cancer MCF-7 cell exosome, and realizes the detection of the tumor cell exosome. A self-calibration sensor for quantitative detection of the tumor exosome is constructed by using MB as a response signal and Fc as a reference.

Abstract: A method for preparing a ratiometric electrochemical miR3123 aptasensor based on a copper-based metal-organic framework (Cu-MOF) composite doped with black phosphorus nanosheets (BPNSs) and thionine (TH) is provided. TH/Cu-MOF is prepared by reacting TH with Cu-MOF precursor, and BPNSs/TH/Cu-MOF is prepared by drop coating the BPNSs and drop coated onto an electrode. A ferrocene (Fc)-labeled single-stranded DNA aptamer is adsorbed on the BPNSs to prepare aptamer-BPNSs/TH/Cu-MOF. Target molecule miR3123 is bonded with the single-stranded DNA aptamer Fc-DNA, Fc-DNA is forced to escape from the BPNSs. Electrochemical signals of Fc are, therefore, weakened while TH signals are slightly affected. The ratiometric electrochemical miR3123 aptasensor is constructed by fitting a linear relationship between peak current intensity ratios IFc/ITH and concentrations of the miR3123.

Abstract: A method for preparing a dual-functional hybrid thin-film for self-calibration detection of tumor-derived exosomes is disclosed. A dual-functional hybrid thin-film, aptamer-BPNSs/Fc/ZIF-67/ITO, is constructed by facile self-assembly of a cobalt-based metal-organic framework (ZIF-67) composite doped with black phosphorus nanosheets (BPNSs), an aptamer and ferrocene (Fc) on an indium tin oxide (ITO) electrode. Methylene blue (MB) labeled aptamer specifically binds to CD63 protein to precisely capture protein. The protein is a specific biomolecule carried by breast cancer MCF-7 cell exosome, and realizes the detection of the tumor cell exosome. A self-calibration sensor for quantitative detection of the tumor exosome is constructed by using MB as a response signal and Fc as a reference.

Abstract: A method for preparing a ratiometric electrochemical miR3123 aptasensor based on a copper-based metal-organic framework (Cu-MOF) composite doped with black phosphorus nanosheets (BPNSs) and thionine (TH) is provided. TH/Cu-MOF is prepared by reacting TH with Cu-MOF precursor, and BPNSs/TH/Cu-MOF is prepared by drop coating the BPNSs and drop coated onto an electrode. A ferrocene (Fc)-labeled single-stranded DNA aptamer is adsorbed on the BPNSs to prepare aptamer-BPNSs/TH/Cu-MOF. Target molecule miR3123 is bonded with the single-stranded DNA aptamer Fc-DNA, Fc-DNA is forced to escape from the BPNSs. Electrochemical signals of Fc are, therefore, weakened while TH signals are slightly affected. The ratiometric electrochemical miR3123 aptasensor is constructed by fitting a linear relationship between peak current intensity ratios IFc/ITH and concentrations of the miR3123.

Abstract: A method for preparing a nanohybrid used for ratiometric fluorescence and ratiometric electrochemical sensing simultaneously is provided. Surface-aminated (—NH2) SiO2 nanospheres encapsulating an electroactive material A or B are prepared and conjugated with surface-carboxylated (—COOH) carbon dots (CDs) or gold nanoclusters (AuNCs) to prepare a conjugate, and the conjugate is conjugated with a DNA aptamer terminated with —NH2. Ions or biomolecules are added to two types of DNA-conjugate dispersions, and ratiometric florescence sensing is realized by fitting the linear relationship between ratiometric fluorescent peak intensity ICDs/IAuNCs and a specific ion concentration or a specific biomolecule concentration.

Abstract: A method for preparing a nanohybrid used for ratiometric fluorescence and ratiometric electrochemical sensing simultaneously is provided. Surface-aminated (—NH2) SiO2 nanospheres encapsulating an electroactive material A or B are prepared and conjugated with surface-carboxylated (—COOH) carbon dots (CDs) or gold nanoclusters (AuNCs) to prepare a conjugate, and the conjugate is conjugated with a DNA aptamer terminated with —NH2. Ions or biomolecules are added to two types of DNA-conjugate dispersions, and ratiometric florescence sensing is realized by fitting the linear relationship between ratiometric fluorescent peak intensity IcDs/IAuNcs and a specific ion concentration or a specific biomolecule concentration.

Abstract: A method for preparing an upconversion-luminescence flexible hybrid membrane for visual detection of tumor markers is provided. Metal ion doped black phosphorus quantum dots (M-BPQDs) are prepared by adopting ultrasonic and solvothermal processes; mesoporous SiO2 grows on the surfaces of the M-BPQDs and amination modification is performed; the M-BPQDs are connected with carboxylated single-stranded DNA1; receptor molecules enter pores; single-stranded DNA2 aptamers and the DNA1 are combined due to base complementation to encapsulate receptors in the pores; and an M-BPQDs probe is prepared. DNA1 terminal-SH and a composite membrane are formed by assembling polymethyl methacrylate-polyimide-gold nanoparticles in a layer-by-layer manner bound by Au—S bonds, and the membrane and the probe are connected to construct the flexible hybrid membrane. The new flexible hybrid membrane is simple and inexpensive to prepare and is highly sensitive.

Abstract: A method for preparing a ratiometric fluorescent sensor for paracetamol based on a copper nanoclusters-carbon dots-arginine composite is provided. Copper nanoclusters CuNCs with red fluorescence are bonded to carbon dots (CDs) with blue fluorescence by electrostatic adsorption and hydrogen bonding, and then arginine is added to form the CuNCs-CDs-arginine composite. The addition of arginine leads to a significant decrease in the blue fluorescence of the CDs, while after the paracetamol is added, the blue fluorescence of the CDs gradually recovered as a result of the specific binding of arginine to paracetamol. The ratiometric fluorescent sensor for paracetamol is constructed by taking the fluorescence of the CuNCs as a reference signal, and the fluorescence of the CDs as a response signal, and fitting the linear relationship between the ratios ICDs/ICuNCs of fluorescence emission peak intensities of CDs and CuNCs and the molar concentrations of paracetamol.

Abstract: A method for preparing a ratiometric fluorescent probe for melamine based on a DNA-stable silver nanocluster-rhodamine 6G complex, wherein the electrostatic self-assembly technology is adopted to construct a silver nanocluster-rhodamine 6G complex. The melamine forms a strong hydrogen bond with thymine in the DNA of the surface of the silver nanocluster, causing rhodamine 6G to dissociate from the surface of the silver nanocluster, destroying the fluorescence resonance energy transfer, so as to restore the fluorescence of the silver nanocluster. This process has little effect on Rhodamine 6G fluorescence which can be used as a reference signal, while silver nanocluster fluorescence can be used as a response signal. By fitting the linear relationship between the ratio of fluorescence emission peak intensities of the silver nanocluster to rhodamine 6G and the molar concentration of the melamine, the ratiometric fluorescent probe for melamine can be constructed.

Abstract: A method for preparing an upconversion-luminescence flexible hybrid membrane for visual detection of tumor markers is provided. Metal ion doped black phosphorus quantum dots (M-BPQDs) are prepared by adopting ultrasonic and solvothermal processes; mesoporous SiO2 grows on the surfaces of the M-BPQDs and amination modification is performed; the M-BPQDs are connected with carboxylated single-stranded DNA1; receptor molecules enter pores; single-stranded DNA2 aptamers and the DNA1 are combined due to base complementation to encapsulate receptors in the pores; and an M-BPQDs probe is prepared. DNA1 terminal-SH and a composite membrane are formed by assembling polymethyl methacrylate-polyimide-gold nanoparticles in a layer-by-layer manner bound by Au—S bonds, and the membrane and the probe are connected to construct the flexible hybrid membrane. The new flexible hybrid membrane is simple and inexpensive to prepare and is highly sensitive.

Abstract: A method for preparing a ratiometric fluorescent probe for melamine based on a DNA-stable silver nanocluster-rhodamine 6G complex, wherein the electrostatic self-assembly technology is adopted to construct a silver nanocluster-rhodamine 6G complex. The melamine forms a strong hydrogen bond with thymine in the DNA of the surface of the silver nanocluster, causing rhodamine 6G to dissociate from the surface of the silver nanocluster, destroying the fluorescence resonance energy transfer, so as to restore the fluorescence of the silver nanocluster. This process has little effect on Rhodamine 6G fluorescence which can be used as a reference signal, while silver nanocluster fluorescence can be used as a response signal. By fitting the linear relationship between the ratio of fluorescence emission peak intensities of the silver nanocluster to rhodamine 6G and the molar concentration of the melamine, the ratiometric fluorescent probe for melamine can be constructed.

Abstract: A method for preparing a ratiometric electrochemical aptasensor for vanillin based on an aptamer-gold nanoparticle-ferrocene-Ketjenblack-ZIF-8 nanocomposite modified electrode includes, dripping ZIF-8 nanocomposite doped with ferrocene and Ketjenblack on the surface of the bare glassy carbon electrode, and immersing this modified electrode in the chloroauric acid solution. The cyclic voltammetry is employed to scan and electrodeposit gold nanoparticles to obtain the gold nanoparticle-deposited ZIF-8 nanocomposite. The aptamer of vanillin is attached to gold nanoparticles via Au—S bonds to construct an aptamer-coupled nanocomposite sensing platform. Then, the electrochemical curves in the presence of different vanillin concentrations are measured, the linear relationship between the ratios of the current peak intensities of ferrocene and vanillin and the molar concentrations of vanillin is fitted, and the ratiometric electrochemical aptasensor for vanillin is constructed.

Abstract: A method for preparing a ratiometric fluorescent probe for cymoxanil based on a double-emission quantum dot-silver nanoparticle complex, wherein, the double-emission carbon quantum dots and the silver nanoparticles are prepared, and the inner filter effect occurring between the double-emission carbon quantum dots and the dispersed silver nanoparticles causes the blue fluorescence quenching of the carbon quantum dots. However, the specific binding of cymoxanil to silver nanoparticles causes the silver nanoparticles to accumulate, and then the inner filter effect occurring between the double-emission carbon quantum dots and the dispersed silver nanoparticles causes the green fluorescence quenching of carbon quantum dots. In this regard, the linear relationship between the intensity ratio of two fluorescent emission peaks of carbon quantum dots and the molar concentration of cymoxanil is established, and the ratiometric fluorescent probe for cymoxanil is constructed.

Abstract: A method for preparing a ratiometric fluorescent probe for cymoxanil based on a double-emission quantum dot-silver nanoparticle complex, wherein, the double-emission carbon quantum dots and the silver nanoparticles are prepared, and the inner filter effect occurring between the double-emission carbon quantum dots and the dispersed silver nanoparticles causes the blue fluorescence quenching of the carbon quantum dots. However, the specific binding of cymoxanil to silver nanoparticles causes the silver nanoparticles to accumulate, and then the inner filter effect occurring between the double-emission carbon quantum dots and the dispersed silver nanoparticles causes the green fluorescence quenching of carbon quantum dots. In this regard, the linear relationship between the intensity ratio of two fluorescent emission peaks of carbon quantum dots and the molar concentration of cymoxanil is established, and the ratiometric fluorescent probe for cymoxanil is constructed.

Abstract: A method for preparing a ratiometric electrochemical aptasensor for vanillin based on an aptamer-gold nanoparticle-ferrocene-Ketjenblack-ZIF-8 nanocomposite modified electrode includes, dripping ZIF-8 nanocomposite doped with ferrocene and Ketjenblack on the surface of the bare glassy carbon electrode, and immersing this modified electrode in the chloroauric acid solution. The cyclic voltammetry is employed to scan and electrodeposit gold nanoparticles to obtain the gold nanoparticle-deposited ZIF-8 nanocomposite. The aptamer of vanillin is attached to gold nanoparticles via Au—S bonds to construct an aptamer-coupled nanocomposite sensing platform. Then, the electrochemical curves in the presence of different vanillin concentrations are measured, the linear relationship between the ratios of the current peak intensities of ferrocene and vanillin and the molar concentrations of vanillin is fitted, and the ratiometric electrochemical aptasensor for vanillin is constructed.

Abstract: A method for preparing a ratiometric fluorescent sensor for phycoerythrin based on a magnetic molecularly imprinted core-shell polymer is provided. With Fe3O4 magnetic nanoparticles as the core, blue fluorescence-emitting carbon quantum dots (B-CDs) are coupled on the surfaces of Fe3O4 magnetic nanoparticles, and SiO2 shells carrying template molecules (phycoerythrin) are grown on the surfaces of Fe3O4/B-CDs. Then, the molecularly imprinted polymer SiO2-MIPs are obtained by eluting the template molecules, that is, Fe3O4/B-CDs/SiO2-MIPs are obtained. Fluorescence emission spectra of the dispersion of Fe3O4/B-CDs/SiO2-MIPs in the presence of different concentrations of phycoerythrin are measured. By fitting the linear relationship between the ratios Iphycoerythrin/IB-CDs of fluorescence emission peak intensities of phycoerythrin and B-CDs and the molar concentrations of phycoerythrin, the ratiometric fluorescent sensor for phycoerythrin is constructed.

Abstract: A method for preparing a ratiometric fluorescent sensor for paracetamol based on a copper nanoclusters-carbon dots-arginine composite is provided. Copper nanoclusters CuNCs with red fluorescence are bonded to carbon dots (CDs) with blue fluorescence by electrostatic adsorption and hydrogen bonding, and then arginine is added to form the CuNCs-CDs-arginine composite. The addition of arginine leads to a significant decrease in the blue fluorescence of the CDs, while after the paracetamol is added, the blue fluorescence of the CDs gradually recovered as a result of the specific binding of arginine to paracetamol. The ratiometric fluorescent sensor for paracetamol is constructed by taking the fluorescence of the CuNCs as a reference signal, and the fluorescence of the CDs as a response signal, and fitting the linear relationship between the ratios ICDs/ICuNCs of fluorescence emission peak intensities of CDs and CuNCs and the molar concentrations of paracetamol.

Abstract: A method for preparing a label-free aptamer electrochemical sensor of ?-interferon based on a dendrimer/gold nanoparticle/molybdenum disulfide nanocomposite is provided. The nanocomposite is drip-coated on a surface of an electrode to prepare a modified electrode, and a terminal sulfhydryl group of a ?-interferon aptamer chain is connected to the gold nanoparticle via Au—S bond to obtain a nanocomposite-aptamer modified electrode. When ?-interferon is present, the ?-interferon specifically binds to the aptamer chain on the sensor, resulting in the aptamer's hairpin structure being opened and stretched, which can effectively adsorb methylene blue MB in the electrolyte, causing significant enhancement of MB redox signal. A linear relationship between a current intensity of MB oxidation peak and a concentration of the ?-interferon is fitted to construct the label-free aptamer electrochemical sensor of ?-interferon.

Abstract: A method for preparing a label-free aptamer electrochemical sensor of ?-interferon based on a dendrimer/gold nanoparticle/molybdenum disulfide nanocomposite is provided. The nanocomposite is drip-coated on a surface of an electrode to prepare a modified electrode, and a terminal sulfhydryl group of a ?-interferon aptamer chain is connected to the gold nanoparticle via Au—S bond to obtain a nanocomposite-aptamer modified electrode. When ?-interferon is present, the ?-interferon specifically binds to the aptamer chain on the sensor, resulting in the aptamer's hairpin structure being opened and stretched, which can effectively adsorb methylene blue MB in the electrolyte, causing significant enhancement of MB redox signal. A linear relationship between a current intensity of MB oxidation peak and a concentration of the ?-interferon is fitted to construct the label-free aptamer electrochemical sensor of ?-interferon.

Abstract: A method for preparing a ratiometric fluorescent sensor for phycoerythrin based on a magnetic molecularly imprinted core-shell polymer is provided. With Fe3O4 magnetic nanoparticles as the core, blue fluorescence-emitting carbon quantum dots (B-CDs) are coupled on the surfaces of Fe3O4 magnetic nanoparticles, and SiO2 shells carrying template molecules (phycoerythrin) are grown on the surfaces of Fe3O4/B-CDs. Then, the molecularly imprinted polymer SiO2-MIPs are obtained by eluting the template molecules, that is, Fe3O4/B-CDs/SiO2-MIPs are obtained. Fluorescence emission spectra of the dispersion of Fe3O4/B-CDs/SiO2-MIPs in the presence of different concentrations of phycoerythrin are measured. By fitting the linear relationship between the ratios Iphycoerythrin/IB-CDs of fluorescence emission peak intensities of phycoerythrin and B-CDs and the molar concentrations of phycoerythrin, the ratiometric fluorescent sensor for phycoerythrin is constructed.