New Type Quantum Dots As Probes For Ratiometric Fluorescence Detection Of Ascorbic Acid,Phosphate,and ATP

Quantum dots（QDs）,a new class of fluorescent nanomaterial with excellent stability,superior optical performance,tunable photoluminescence,and good resistance to photobleaching,are applied in fields including physics,chemistry,and biology.Fluorescent detection technology has drawn extensive attention because of its high sensitivity.However,the single-signal fluorescence method possesses relatively poor anti-interference ability and is susceptible to interference from background environmental fluctuations.Ratiometric fluorescence with self-calibration property employs the ratio between the reference signal and working signal,which eliminates signal fluctuations induced by the background environment.In this work,by combing QDs and nanomaterials,ratiometric fluorescence methods are established for ascorbic,phosphate,and ATP detection.The study details are as follows:1.A Ratiometric Fluorescence-scattered Light Strategy Based on MoS₂ Quantum dots/CoOOH Nanoflakes System for Ascorbic Acid DetectionA facile ratiometric fluorescence method for ascorbic acid（AA）detection was established by combining the fluorescence of MoS₂ quantum dots（QDs）with second-order scattering（SOS）of CoOOH.In MoS₂ QDs/CoOOH nanohybrid system,the fluorescence of MoS₂ QDs was quenched by CoOOH whereas the intensity of SOS was relatively close to the fluorescence due to the intrinsic high scattering ability of large size CoOOH nanoflakes.With the addition of AA,CoOOH nanoflakes were reduced to Co²⁺accompanied the size decline and the disappearance of characteristic absorption in UV-vis spectrum,resulting in the fluorescence recovery and SOS fading.Thus,the ratiometric detection of AA was obtained through the opposite changes of fluorescence and SOS.Under optimized conditions,the detection limit of AA was 0.21μmol L^-1 with a linear range from 0.80 to 32.0μmol L^-1.Furthermore,the MoS₂ QDs/CoOOH nanohybrid system was applied to the detection of AA in human serum samples and vitamin C tablets with satisfactory results.2.Fluorescence-scattering dual-signal response of carbon dots@ZIF-90 for phosphate ratiometric detectionRatiometric fluorescence has drawn extensive attention owing to its self-calibration property.However,it is difficult to obtain appropriate fluorescent materials that can be excited under one excitation and possess well-resolved signals simultaneously.In this work,with the optical properties of the fluorescence of CDs（carbon dots）and the second-order scattering（SOS）of ZIF-90（zeolitic imidazole frameworks-90）nanoparticles,the synthesized CDs@ZIF-90 can be applied to phosphate(PO₄^3-)ratiometric detection.The fluorescence of CDs is greatly suppressed through encapsulating CDs into ZIF-90.Nevertheless,the SOS is quite obvious due to the high scattering intensity of large size ZIF-90.The competitive coordination between PO₄^3-and the metal node of ZIF-90decomposes CDs@ZIF-90,leading to the restoration of fluorescence and the diminution of SOS.On the basis of the PO₄^3--induced ZIF-90 decomposition and CDs release,a novel method for PO₄^3-ratiometric detection is developed through the dual-signal response of the fluorescence-scattering.Under the optimal condition,the method shows a linear range from 1.0 to 50.0μmol L^-1 with a detection limit of 0.23μmol L^-1.Furthermore,the probes are employed to assess PO₄^3-in practical aqueous samples successfully.Compared with the traditional approach which only records fluorescence signals,the method reported here provides a new strategy to design ratiometric sensors by fluorescence and scattering.3.A ratiometric fluorescence strategy based on dual-signal response of carbon dots and o-phenylenediamine for ATP detectionHerein,a convenient method is developed for ratiometric fluorescence detection of ATP（adenosine triphosphate）based on CDs-OPD（carbon dots-o-phenylenediamine）.In the absence of ATP,oxOPD,the colored oxidation product of OPD fabricated by a redoxreaction occurred between OPD and Cu²⁺,not only quenches the fluorescence of CDs,but also emits a yellow fluorescence which acts as another signal element.However,ATP will compete with OPD to chelate Cu²⁺inhibiting the redoxreaction,which hampers the formation of oxOPD resulting in the diminution of IFE（inner filter effect）between CDs and oxOPD,then the fluorescence of CDs restores.ATP-induced dual-signal response of the CDs-OPD-Cu²⁺system makes ratiometric assay possible.The method shows a linear range from 1.0 to 100.0μmol L^-1 with a detection limit of 0.43μmol L^-1.Furthermore,the semi-quantitative measurement of ATP is available by naked eyes through the color of fluorescence and solution.Finally,the method is employed for the quantification of ATP in adenosine disodium triphosphate tablets and MCF-7 cell lysates with satisfactory results.