Preparation Of Novel SERS Substrates Based On MOFs And Detection Of Histamine In Food

Histamine（HA）is the most toxic biogenic amines（BAs）with potential carcinogenicity.Intake of a certain amount of HA can cause various poisoning reactions and even endanger life.HA is commonly present in a wide range of food products,including fish,meat,and fermented foods.It is often used as a key index to evaluate food quality.Therefore,the development of rapid detection method of HA can provide technical support for the safety of food processing and preservation.Surface-enhanced Raman spectroscopy（SERS）,as a vibrational spectroscopy technology combined with nanotechnology,can provide abundant chemical molecular fingerprint information,and has the advantages of easy operation and low fluorescence background.In the field of SERS analysis,preparing SERS-active substrates with excellent sensing performance is the key to obtaining high-quality spectra.The three types of substrates developed till now show different advantages,such as simple preparation of colloid substrates,high applicability of solid substrates,and diverse performance of functional substrates.However,they still need continuous improvement in terms of detection modes and applicability.Based on the diverse structures and functions of metal-organic frameworks（MOFs）,this study precisely controls the construction of SERS substrates and adopts different types of signal quantification methods to improve the technical problems existing in traditional SERS substrates,and to enhance the applicability of HA detection in different systems.Meanwhile,the optimization of the substrates is continuously carried out to improve the sensitivity and specificity of the method.The details are as follows:1.To improve the poor uniformity and tendency to aggregate of colloid substrates,a ratiometric SERS sensor was constructed using the stability and signal enhancement ability of ZIF-67.A core-shell structure substrate（Au NFs@ZIF-67）was synthesized with Au nanoflowers（Au NFs）as the core and ZIF-67 as the shell.4-mercaptobenzoic acid（4-MBA）was utilized as the recognition molecule and signal correction internal standard（IS）for HA.In the detection system,the Raman characteristic peak intensity(I₁₁₇₂)increased with an increase in HA concentration while the signal intensity of 4-MBA(I₁₀₇₄)remained stable.A positive linear correlation was observed between the ratio value of HA and 4-MBA signals(I₁₁₇₂/I₁₀₇₄)and the logarithmic value of HA concentration in the range of 10^-7M to 10^-3M（the fitting degree R²=0.993）,with a detection limit（LOD）of 0.87×10^-7M.The spiked bass sample demonstrated a recovery rate of 93.42%to 102.23%,and the effective monitoring of fish decay process was realized.2.To improve sample collection density and environmental tolerance of solid substrates,a specific SERS sensor with an indirect detection mode was developed,utilizing the functional tunability and high load capacity of IRMOF-3.In situ synthesis of Au nanoparticles（Au NPs）on IRMOF-3 and carrier preparation with polydimethylsiloxane（PDMS）resulted in the SERS substrate（IRMOF-3@Au/PDMS）.Embedding 5-mercapto-dithiobis（2-nitrobenzoic acid）（DTNB）into Au nanorods with Ag shell（Au NR@Ag）and functionalizing histamine aptamer（HA apt）constructed the signal probe（Au NR-DTNB@Ag-HA apt）.Theπ-πinteraction between HA apt and IRMOF-3 was utilized for the assembly of the SERS substrate and signal probe.In the detection system,due to the higher affinity between HA and HA apt,some signal probes detached from the SERS substrate,leading to a decrease in DTNB signal intensity(I₁₃₃₁).The results demonstrated a good negative linear correlation between I₁₃₃₁and the logarithmic value of HA concentration in the range of 9.0×10^-9M to 3.6×10^-3M（R²=0.990）,with a LOD of 3.23×10^-10M and a recovery of wine samples of 95.90%to 101.00%.3.To simplify the functional substrate preparation process and enhance the detection efficiency,a fast and efficient signal output SERS sensor was designed,using the exceptional catalase-like activity of MIL-100（Fe）.MIL-100（Fe）was loaded with Au NPs to create MIL-100（Fe）@Au NPs nanocomposites,forming a"catalyst"in a catalytic reaction system with 5-tetramethylbenzidine（TMB）and hydrogen peroxide（H₂O₂）.Additionally,Ag nanoparticles（Ag NPs）were synthesized and used as a"signal booster"for the catalytic products of TMB.Following nucleic acid functionalization,the"catalyst"and"signal booster"were assembled by complementary pairing of nucleic acid chain bases to form a"satellite"structure.In the detection system,the specific binding of HA and HA apt caused a reduction in the amount of Ag NPs on MIL-100（Fe）@Au NPs,resulting in a corresponding decrease of ox TMB signal intensity(I₁₆₀₄).The results indicated that I₁₆₀₄showed good negative linearity with the logarithmic value of HA concentration in the range of 10^-11M to0.5×10^-2M（R²=0.996）,with a low LOD of 0.39×10^-11M and a recovery rate of fermented soybean products of 94.42%to 105.75%.