In this study, we synthesized gold nanoparticles (AuNPs) in situ on the surface of two-dimensional Cu-TCPP (meso-tetra(4-carboxyphenyl)porphine) metal– organic framework (MOF) nanosheets to produce AuNP@Cu-TCPP nanocomposites as surface-enhanced Raman scattering (SERS) substrates. The SERS signal was enhanced in two ways: aggregation of the AuNPs@Cu-TCPP near the SERS hotspot through the strong adsorption capacity of the MOF, and the synergistic effect between the charge-transfer enhancement of the Cu-TCPP MOF and the electromagnetic enhancement of plasmonic metal AuNPs. The SERS activity of AuNPs@Cu-TCPP was evaluated by the analysis of multiple model analytes; Rhodamine 6G (R6G) and benzidine were detected with detection limits below 10 –13 and 10 –12 mol·L –1 , respectively. We used AuNP@Cu-TCPP as a SERS substrate combined with an enzyme-linked immuno- sorbent assay (ELISA) to detect the tumor marker carboxylesterase 1 (hCE1) in human serum. The SERS signal of benzidine at 1609 cm −1 is linearly correlated with hCE1 in the concentration range of 0.1–120 ng·mL −1 . Owing to their high sensitivity and excellent SERS sensing capability, AuNPs@Cu-TCPP nanocomposites have potential applicability in the analysis of clinical samples.
By in situ synthesis of gold nanoparticles (AuNPs) within the acid-etched (AE) MIL-101 (Cr) framework, AE-MIL-101 (Cr) nanocomposites embedded with AuNPs (AuNP/AE-MIL-101 (Cr)) were prepared as surface-enhanced Raman scattering (SERS) substrate. AuNPs are uniformly distributed and stabilized inside the metal-organic framework (MOF), thus forming more SERS hotspots. The SERS performance of AuNP/AE-MIL-101 (Cr) was evaluated using 4-mercaptophenylboronic acid (4-MPBA), 4-mercaptobenzoic acid (4-MBA), benzidine, and rhodamine 6G (R6G). The SERS substrate displays satisfying stability with very low background signal. When benzidine is used as the Raman reporter, the limit of detection (LOD) can reach 6.7 × 10 −13 mol·L −1 , and the relative standard deviation (RSD) of the intra- and inter-batch repetitive tests is less than 5.2%. On this basis, we developed a method for the detection of human carboxylesterase 1 (hCE 1) in human serum using AuNP/AE-MIL-101 (Cr) nanocomposite as SERS substrate and enzyme-linked immunosorbent assay (ELISA) colorimetric substrate as SERS marker. This method was used to determine hCE 1 in clinical serum samples without complicated sample pretreatment, and the detection results were consistent with the data determined by ELISA. In the concentration range 0.1–120 ng·mL −1 , the SERS signal intensity of benzidine at 1609 cm −1 gradually decreases with the increase of hCE 1 concentration (R 2 = 0.9948). The average recoveries of hCE 1 in human serum are in the range 84 to 108%, with RSDs lower than 7.7%. Graphical abstract
By using AuNP/acid etching-MIL-101(Cr) metal organic framework (MOF) as SERS substrate and enzyme-linked immunosorbent assay (ELISA) colorimetric substrate as the SERS marker, a rapid and sensitive method for the determination of human carboxylesterase 1 (hCE1) in human serum samples has been developed.
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