| Amino acid is a major index to measure the growth of animals and plants and food quality,and its concentration is related to the food quality.It can also be used as an evaluation index for screening and diagnosing genetic metabolic diseases.Therefore,the analysis of amino acids is of great significance to biomedicine and food health.Nowadays,with the continuous development of nanoscience and spectroscopy technology,surface-enhanced Raman spectroscopy(SERS)uses the interaction between light and nanostructured materials to significantly enhance the Raman signal of molecules adsorbed on nanostructured surfaces,obtaining the fingerprints of samples or Raman probe molecules in a super-sensitive way.With some unique advantages such as non-invasiveness,high sensitivity,good selectivity,fast analysis speed,and low water interference,SERS has become an extremely promising technology for life science and clinical testing applications.Due to the small Raman scattering cross-sectional area of amino acids,it is difficult to direct detect their SERS signals.In order to solve this issue,we developed a kind of specific chemical reaction and highly sensitive SERS substrate.Also,homocysteine,histidine,and tryptophan were chosen as research objects to further explore the application of SERS strategies in biomedicine and food analysis,and their specific quantitative detections were realized.This work provides a new analytical method for amino acids in clinical disease diagnosis and food inspection technology.This thesis was mainly carried out in the following aspects:1.Homocysteine(Hcy)is a sensitive index of vascular damage.Improper metabolism of Hcy can lead to Alzheimer's disease,cancer,cardiovascular disease and so on.However,sensitive and efficient determination of Hcy remains an extremely big challenge for many researchers.Herein,we present an Hcy sensing strategy based on SERS along with a specific reaction of o-phthalaldehyde(OPA)and Hcy.The obtained adduct 2-(1-carboxyl-3-thiopropyl)-1-isoindolinone(Hcy-OPA)can be directly detected by SERS using gold nanoparticles(Au NPs)as the substrate.The developed method displays a broad linear range(5.0×10-10-5.0×10-6mol/L)and a low detection limit(4.8×10-11mol/L),which is superior to those of the reported detection methods.Moreover,it can selectively detect Hcy in bovine serum samples with a concentration as low as 5.0×10-9mol/L over the interference of the other amino acids and glutathione.2.Histidine(His)is widely used in the field of food and medicine.However,sensitive and efficient detection of His is still a challenge for many researchers.In this chapter,based on the former design,the SERS mehtod combined with the specific reaction of OPA and His was still used to detect His.The inositol hexaphosphate wrapped gold nanoparticles(IP6@Au NPs)were used as the substrate.Since the outer layer of the gold nanoparticles was wrapped with inositol hexaphosphate,it could isolate the interference of the external salt solution,preventing the aggregation of nanoparticles which hinders the detection.Also,since the imidazole ring remains unchanged in the reaction,the-NH-on the imidazole ring can be closely combined with the gold nanoparticles,which greatly enhances the Raman signals and enables the direct detection of the His-OPA adduct in SERS.The developed method has good selectivity,a wide linear range(5.0×10-8mol/L-5.0×10-5mol/L),and a detection limit of 9.7×10-10mol/L.With the developed method,the determination of His in milk samples were realized.3.Tryptophan(Trp)plays a vital role in the nervous system,the reduction of Trp levels may lead to pellagra.If metabolism is abnormal,toxic products will accumulate in the brain,leading to hallucinations,schizophrenia,drowsiness,nausea,and other symptoms.Therefore,it is necessary to invent a sensitive and efficient method to detect Trp.For this purpose,a highly sensitive two-dimensional SERS substrate(AAO/IP6@Ag NPs)was prepared.Anodized aluminum oxide(AAO)assembled silver inositol hexaphosphate nanoparticles(IP6@Ag NPs)was used to replaced the sol system to detect Trp,making SERS detection reliable and uniform.The reason is that inositol hexaphosphate can well chelate with aluminum and also prevent the oxidation and aggregation of silver nanoparticles,making the substrate more stable.Most importantly,the uniform and porous structure of AAO can ensure the consistency of signal intensity.Therefore,on the basis of former chapter,the uniformity was enhanced.The developed method has a linear relationship between1.0×10-8mol/L-1.0×10-4mol/L,a detection limit of 4.2×10-9mol/L,and a good selectivity. |
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