Construction And Application Of Optical Biosensor Systems Based On Carbon Dots And Metal Nanoparticles

Organisms contain various ions,small biological molecules and biological macromolecules.They all play very important roles in life activities.Small biological molecules such as uric acid,it is the final product of purine catabolism.Excessive uric acid production or uric acid excretion dysfunction will lead to excessive retention of uric acid in the body,which will lead to gout.In addition,chronic nutritional deficiency of ascorbic acid can cause symptoms of scurvy.Ascorbic acid oxidase can oxidize ascorbic acid to produce water and dehydroascorbic acid.Understanding the stability and catalytic activity of ascorbic acid oxidase is of great significance to prevent the degradation of ascorbic acid in fruits and vegetables.Based on the above,two optical probes were constructed to detect uric acid,ascorbic acid and the activity of ascorbic acid oxidase owning to the special optical properties of nanomaterials.We obtained the following results through a series of characterization and experimental studies:1.A dual-read bioprobe for the detection of uric acid was constructed by combining nitrogen-doped carbon quantum dots with silver triangular nanoprism.Among them,nitrogen-doped carbon quantum dots were used for fluorescence signal output,while silver triangular prism was used for colorimetric signal output and as fluorescence quenching agent for nitrogen-doped carbon quantum dots.The probe was characterized by transmission electron microscopy,dynamic light scattering,infrared spectroscopy,Zata potential,X-ray photoelectron spectroscopy,fluorescence spectrophotometer and ultraviolet-visible spectrophotometer.The results show that the fluorescence of nitrogen-doped carbon quantum dots was quenched by silver triangular nanoprism due to the internal filtration effect.Hydrogen peroxide etched the silver triangular prism into a circular nanodisk,and the probe of fluorescence recovered.In the presence of uric acid,uric acid can bind to the side of silver triangle nanoprism to effectively protect silver triangle nanoprism from etching.The fluorescence intensity of nitrogen-doped carbon quantum dots measured at 440 nm decreases with the increase of uric acid concentration,while the absorbance of silver triangular nanoprism measured at 683 nm increases.Experiments show that the dual-read probe has a good linear range.The fluorescence method works in the range of 1⁴2?M uric acid concentration,and the colorimetric method works in the range of 0.1⁴5?M uric acid concentration.The detection limits of the two methods were 200 and 50 nM,respectively.In addition,the dual-read probe shows a good selectivity for uric acid and has potential applications in practical analysis.2.Based on the oxidation of o-phenylenediamine by potassium permanganate,the oxidation product of o-phenylenediamine exhibits yellow fluorescence emission at 565nm and an absorption peak at 425 nm.A dual-mode biosensor was constructed to detect ascorbic acid and ascorbic acid oxidase activity using carbon dots and o-phenylenediamine oxide.The probe combines the advantages of ratio fluorescence and colorimetry.The probe was characterized by high power transmission electron microscopy,dynamic light scattering,infrared spectroscopy,Zata potential,time-dependent single photon counting,X-ray photoelectron spectroscopy,fluorescence spectrophotometer and ultraviolet-visible spectrophotometer.O-phenylenediamine oxide quenches the fluorescence of carbon dots at 450 nm by fluorescence resonance energy transfer.When ascorbic acid was added beforehand,ascorbic acid consumed potassium permanganate to inhibit the formation of oxidized o-phenylenediamine.With the increase of ascorbic acid concentration,the fluorescence intensity of oxidized o-phenylenediamine at 565 nm decreased and that of carbon dots at 450 nm increased.At the same time,the color of the solution changed from yellow to colorless.Contrary to ascorbic acid detection,ascorbic acid can be oxidized by ascorbic acid oxidase,which resulted in fluorescence and color changes in the opposite direction when ascorbic acid oxidase activity was measured.That was the fluorescence ratio(I₅₆₅/I₄₅₀)increased and the solution color changed from colorless to yellow.Therefore,the fluorescence intensity ratio(I₅₆₅/I₄₅₀)and colorimetric"bare-eye"readout can be used to determine ascorbic acid concentration and ascorbic acid oxidase activity.The linear range of ascorbic acid fluorescence assay was 0.6⁴0?M and the colorimetric assay was 0.2⁷0?M.The linear ranges of fluorescence and colorimetric detection of ascorbic acid oxidase were 0.04⁵mU·mL^-1 and 0.04⁸ mU·mL^-1,respectively.The detection limits of ascorbic acid were 9and 40 nM,and the LODs for ascorbic acid oxidase activity were 0.017 and 0.012mU·mL^-1 respectively.