Construction Of Highly Stable MOF Nanoplates Based On Dicarboxylic Acid Ligands And The Application In Electrochemiluminescence Biosensors

Metal organic frameworks?MOFs?are a prevailing class of solid porous materials.Due to their large specific surface area,significant porosity,and easy adjustment and modification of pore channels,MOFs have potential applications in the fields of gas storage and separation,drug transportation,catalysis,and sensing,which has attracted more and more attention and research interest.Recently,MOFs have been used as carrier materials to increase the immobilization capacity of ECL luminophores to develop sensitive electrochemiluminescence?ECL?biosensors.However,due to the water unstability of most MOFs,the luminophores are easy to leak when we are detecting,which affects the stability of ECL sensors.Moreover,the diffusion paths of the ions,electrons,coreactant and coreactant intermediates in the three-dimensional?3D?bulk MOFs were greatly long,which limit the excitation of the internal luminophores and thus led to reducing the ECL efficiency and utilization ratio of the luminophores.In addition,most of the previously reported methods for immobilizing luminophores in MOFs were post-modification,which were complicated and difficult to operate.Based on the above points,the ECL luminophores were used as bridging ligands,and they were directly fixed into the two-dimensional?2D?MOF nanoplates through strong coordination bonds.Then,the synthesized 2D MOF nanoplates were used as ECL signals to construct a series of biosensors with excellent ECL performances,achieving ultra-sensitive detection of targets.This method not only opens a new way for designing highly stable and sensitive ECL biosensors,but also extends the application of two-dimensional MOF nanoplates in the field of ECL and bioanalysis.The main research contents of this article are as follows:Part 1 Study on the construction of electrochemiluminescence biosensor based on metal organic nanosheets doped with ruthenium complexIn this study,a novel Ru?bpy?₂?dcbpy?-doped two-dimensional?2D?metal-organic framework?MOF?nanoplate?Ru@Zr12-BPDC,BPDC=4,4'-biphenyldicarboxylate,bpy=2,2'-bipyridine,H₂dcbpy=2,2'-bipyridine-5,5'-dicarboxylic acid?with outstanding ECL performance was synthesized via a mixed ligand strategy.The identical lengths between Ru?bpy?₂?dcbpy?and BPDC ligands allowed the Ru?bpy?₂?dcbpy?to connect two Zr₁₂2 clusters of Ru@Zr₁₂-BPDC nanoplate through strong coordination bonds,which not only resulted in the improvement of the immobilization content of Ru?bpy?₂?dcbpy?,but also stopped the leakage of the Ru?bpy?2?dcbpy?effectively.In addition,the ultrathin nature and high porosity of 2D Ru@Zr₁₂-BPDC nanoplate not only allowed the electrochemical activation of the external and internal Ru?bpy?₂?dcbpy?,but also greatly shortened the diffusion distance of the electrons,ions,coreactant?tripropylamine,TPrA?and coreactant intermediates?TPrA·and TPrA·⁺?.The reasons above made more interior Ru?bpy?₂?dcbpy?could be excited and thus result in increasing utilization ratio of the luminophores.Because of the above merits,the Ru@Zr12-BPDC nanoplate exhibited high and stable ECL emission,and thus was employed to construct an aptasensor for ultrasensitive detection of mucin 1?MUC1?.To further enhance the sensitivity of the proposed aptasensor and amplify signal,the target MUC1 was converted into the H1-H2 duplex with the assistance of H1,H2 and MUC1-catalyzed hairpin assembly?CHA?.As expected,the proposed aptasensor exhibited remarkable stability,excellent sensitivity,and displayed a wide liner range from 1 fg/mL to 10 ng/mL with a low detection limit of 0.14 fg/mL.As far as we know,the construction of an ECL biosensor based on ruthenium complex doped 2D MOF nanoplates is the first example.This study demonstrated that the use of ruthenium complex doped MOF nanoplates to increase the ECL stability and intensity is an efficient strategy for the construction of highly stable and sensitive ECL biosensors,and therefore may extend the applications of 2D MOF nanoplates in ECL and bioanalysis fields.Part 2 Research on the construction of biosensors based on the restriction of intramolecular motion?RIM?by MOF to enhance electroluminescenceHerein,a new phenomenon of enhanced electrochemiluminescence?ECL?emission by restricting intramolecular motion in the 2D ultra-thin Zr₁₂-adb?adb=9,10-anthracene dibenzoate?metal-organic framework?MOF?nanoplate was discovered for the first time.The coordination immobilization of adb in porous ultra-thin Zr₁₂-adb nanoplate endowed the Zr₁₂-adb excellent ECL performance,including stronger ECL signal and higher ECL efficiency relative to those of H₂adb monomers and H₂adb aggregates.In the 2D Zr₁₂-adb nanoplate,the bridging ligand adb was stretched and fixed between two Zr₁₂2 clusters,which restricted intramolecular rotations and suppressed unnecessary energy loss caused by self-rotation,thereby remarkably improved the ECL intensity and efficiency.More importantly,the porous ultra-thin structure of Zr₁₂-adb MOF nanoplate not only allowed the coreactants to diffuse into the MOF interior,making both internal and external adb be excited,but also shortened the migration distance of electrons,ions,coreactants and coreactant intermediates,which further improved the ECL efficiency of Zr₁₂-adb and overcame the shortcoming of H₂adb aggregates in which the internal luminophores were not easily excited.Regarding the excellent ECL properties above,Zr12-adb nanoplate was selected as a new ECL emitter incorporated with the bipedal walking molecular machine together to fabricate a biosensor for sensitive detection of mucin 1.The enhanced ECL by restriction of intramolecular motions in MOFs provided a new pathway to improve ECL intensity and efficiency,which lighted up a lamp for the design and manufacture of high-performance ECL materials based on MOFs,thus offering new opportunities to develop ultrasensitive ECL biosensors.