Metal-organic framework modified by silver nanoparticles for SERS-based determination of sildenafil and pioglitazone hydrochloride

Breakthrough in plasmonic enhanced MOFs: Design, synthesis, and catalytic mechanisms for various photocatalytic applications

Integrating metal-organic framework MOFs with plasmonic nanoparticles (NPs) addresses a significant shortcoming of standard plasmonic platforms: their low efficacy with non-adsorbing compounds. The corporation of porous MOFs complements the plasmonic characteristics, allowing for a broader range of applications. This study highlights recent advancements in the design, synthesis, structural engineering, and functional properties of heterostructures combining plasmonic NPs with MOFs, focusing on their plasmonic and catalytic reaction behaviors. These developments have greatly enhanced the protentional of plasmonic NPs-MOFs heterojunction in nanofabrication and various applications, such as chemical sensing techniques like localized surface plasmon resonance (LSPR) surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorbance (SEIRA). Additionally, the study thoroughly examines the interface interaction and photocatalytic performance of plasmonic NPs-MOFs. Various practical applications of plasmonic NPs-MOFs heterojunction are explored, including their promising role in tackling environmental challenges like industrial water pollution. Furthermore, we have a detailed discussion of various photocatalysis processes, including water splitting, CO2 reduction, pollutant degradation, and various sensing applications. Identifying current limitations and outlining future research directions to bridge existing knowledge gaps, including interface interaction, photocatalytic performance, and practical applications providing a comprehensive understanding, are the main aims of this review to inspire the development of next-generation plasmonic NPs-MOFs materials. It concludes by discussing future directions and challenges in composite development, emphasizing their potential to provide sustainable and efficient solutions for environmental remediation and energy conversion.

An aptamer sensor based on AgNPs@MOF for surface-enhanced Raman spectroscopy detection of sulfadimethoxine in food

A highly sensitive aptamer sensor (aptasensor) is proposed based on metal-organic frameworks-silver nanoparticles (AgNPs@MOF) to detect sulfadimethoxine (SDM) by surface-enhanced Raman spectroscopy (SERS). AgNPs@MOF with SERS activity was successfully fabricated by synthesizing AgNPs in situ on the surface of MIL-101(Fe), and SDM aptamer and Raman reporter 4-aminophenthiophenol (4-ATP) were selected as specific recognition elements and signal probes, respectively. When SDM was absent, the SDM aptamers were effectively adsorbed on the surface of AgNPs@MOF, thus keeping AgNPs@MOF in a dispersed state, resulting in a weakened SERS signal of 4-ATP. In the presence of SDM, the combination of SDM and aptamer formed a rigid hairpin SDM-aptamer complex, which bound less to AgNPs@MOF. Therefore, fewer aptamers were adsorbed on AgNPs@MOF, which exposed more hot spots, resulting in an enhanced SERS signal of 4-ATP. The aptasensor had good selectivity and sensitivity towards SDM and a good linear relationship between SERS intensity and SDM concentration in the range 6.00-150.00 ng/mL, with the limit of detection as low as 2.73 ng/mL. Further application to honey and chicken samples spiked with SDM resulted in satisfactory recoveries, and the aptasensor showed good stability and reproducibility in real samples. The aptasensor based on AgNPs@MOF was proposed for the first time to detect trace SDM by SERS, which provided a favorable way to develop various sensing platforms for antibiotic detection in food safety.

Paper-Based Aptasensor Assay for Detection of Food Adulterant Sildenafil

Sildenafil is used to treat erectile dysfunction and pulmonary arterial hypertension but is often illicitly added to energy drinks and chocolates. This study introduces a lateral flow strip test using aptamers specific to sildenafil for detecting its illegal presence in food. The process involved using graphene oxide SELEX to identify high-affinity aptamers, which were then converted into molecular gate structures on mesoporous silica nanoparticles, creating a unique signaling system. This system was integrated into lateral flow chromatography strips and tested on buffers and chocolate samples containing sildenafil. The method simplifies the lateral flow assay (LFA) for small molecules and provides a tool for signal amplification. The detection limit for these strips was found to be 68.2 nM (31.8 µg/kg) in spiked food samples.

Highly sensitive colorimetric and paper-based detection for sildenafil in functional food based on monodispersed spherical magnetic graphene composite nanozyme

BACKGROUND

Sildenafil (SIL) is regarded as an illegal adulterant in functional foods. Some functional foods doped with SIL have posed significant concern about their safety risks. However, the facile colorimetric detection of SIL is rarely investigated.

RESULTS

Herein, we prepared a monodispersed spherical composite nanozyme (Fe3O4-NH2/GONRs), possessing excellent peroxidase-like (POD-like) and catalase-like (CAT-like) activities and strong superparamagnetic property. The enzyme-like activities of Fe3O4-NH2/GONRs can be selectively inhibited by SIL due to the synergistic effect of hydrogen bonds and π-π stacking between Fe3O4-NH2/GONRs and SIL. Leveraging this mechanism, a highly sensitive and selective colorimetric detection for SIL with a detection limit (LOD) of 0.26 ng/mL was developed. In addition, we prepared a three-dimensional paper-based analytical device (3D-PAD) for SIL colorimetric detection with naked-eyes and the semi-quantitative analysis with a LOD of 88 ng/mL.

SIGNIFICANCE

The proposed colorimetric and PAD detections demonstrated the advantages of low-cost, highly sensitive and selective, thus have promise application potential in the rapid detection of adulterated functional foods.

Recent advances of MOF-based SERS substrates in quantitative analysis of food contaminants: a review

Advancements in food-contaminant detection technologies can significantly improve food safety and human health. Surface-enhanced Raman spectroscopy (SERS) has become the preferred analytical method for food-safety detection owing to its numerous advantages, which include unique 'molecular fingerprinting' features, high sensitivity, rapid responses, and non-invasive characteristics. Raman-signal enhancements rely heavily on high-performance SERS substrates. In recent years, metal-organic framework (MOF)-based SERS substrates have gained attention as promising candidates for developing SERS technologies owing to their distinctive structures and functions. This review comprehensively examines recent advances in MOF-based SERS substrates, focusing on the main role of MOFs in SERS substrates as well as their typical categories and structures, construction methods, and representative applications in food-contaminant detection. First, the primary roles of MOFs in SERS substrates are briefly introduced. Next, a comprehensive overview of the typical categories and structures of MOF-based SERS substrates is discussed. Subsequently, a fundamental view of the general construction methods for MOF-based SERS substrates is presented. Next, the main applications of MOF-based SERS substrates for food-contaminant detection are summarised. Finally, challenges and perspectives, including improvements in SERS performance and stability, and the unification of SERS mechanisms, are addressed and discussed.

Innovative utilization of silver nanoparticles localized surface plasmon resonance for green and sensitive spectrofluorimetric analysis of sildenafil and xipamide in pure forms and pharmaceutical preparations

A green, novel, simple and sensitive spectrofluorimetric approach was investigated and validated for the analysis of two important cardiovascular drugs namely; sildenafil citrate and xipamide using silver nanoparticles as a fluorescence probe (Ag-NPs). Silver nanoparticles were prepared through chemical reduction of silver nitrate using sodium borohydride in distilled water without using non-green organic stabilizer. These nanoparticles were stable, water soluble and had high fluorescence. After addition of the studied drugs, noticeable quenching of Ag-NPs fluorescence occurred. The intensity of Ag-NPs fluorescence was measured at 484 nm (λex 242 nm) before and after complex formation with these studied drugs. The difference between these values (ΔF) were linear with the concentrations in the following ranges (1.0-10.0 μg/mL), (0.5-5.0 μg/mL) for sildenafil and xipamide, respectively. The formed complexes did not need to be separated by solvent extraction before measurement. For proving the complex formation between the two studied drugs and silver nanoparticles, stern volmer method was applied. The suggested method was perfectly validated in compliance with the international conference on harmonization (ICH) Guidelines and the outcomes were acceptable. Furthermore, suggested technique was perfectly applied for the assay of each drug in its pharmaceutical dosage form. Eventually assessment of method greenness was performed using different tools and found that the suggested method was safe and eco-friendly.

Fabrication of molecularly-imprinted gold nanoparticle-embedded Fe-MOFs for highly selective SERS detection of 17β-estradiol in milk

17β-Estradiol (17β-E2) could accumulate in humans through milk, thus causing diseases by interfering with the function of the endocrine system. However, its detection at a trace level in milk is still a challenge because of matrix interferences. In this work, a core-shell structured polydopamine molecular-imprinted gold nanoparticles (AuNP@MIP-PDA) were embedded into Fe metal-organic framework materials to form a well-defined hexagonal microspindle structure of AuNP@MIP-PDA@MIL-101(Fe). AuNP@MIP-PDA were successfully encapsulated within the MIL-101 crystals through the hydrophobic interaction between organic ligands and the aromatic groups of PDA, the chelating power of catechol groups, as well as the introduction of acetic acid. Combined with the SERS activity of AuNPs, the specific recognition sites from MIPs, and the adsorption and enrichment capability of MIL-101, the fabricated nanohybrids could be designed as highly selective SERS sensors for the detection. By effectively preventing the macromolecule adsorption and the preconcentration of 17β-E2 near the SERS-active surface, the SERS sensor could be directly applied in the selective detection of 17β-E2 in milk without tedious pretreatment. The method demonstrated an outstanding detection limit of 1.95 × 10^-16 mol L^-1, without the interference mainly originating from the two analogues, estrone and estriol. These promising results foresee the potential application of this novel MIP-based SERS sensor in food and environmental sensing.

Determination of pioglitazone hydrochloride by flow injection chemiluminescence tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex system

A novel flow injection-chemiluminescence (FI-CL) approach is proposed for the assay of pioglitazone hydrochloride (PG-HCl) based on its enhancing influence on the tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex (Ru(bipy)₃ ²⁺ -DPA) CL system in sulfuric acid medium. The possible CL reaction mechanism is discussed with CL and ultraviolet (UV) spectra. The optimum experimental conditions were found as: Ru(bipy)₃ ²⁺ , 5.0 × 10^-5  M; sulfuric acid, 1.0 × 10^-3  M; diperiodatoargentate(III) (DPA), 1.0 × 10^-4  M; potassium hydroxide, 1.0 × 10^-3  M; flow rate 4.0 ml min^-1 for each flow stream and sample loop volume, 180 μl. The CL intensity of PG-HCl was linear in the range of 1.0 × 10^-3 to 5.0 mg L^-1 (R²  = 0.9998, n = 10) with limit of detection [LOD, signal-to-noise ratio (S/N) = 3] of 2.2 × 10^-4  mg L^-1 , limit of quantification (LOQ, S/N = 10) of 6.7 × 10^-4  mg L^-1 , relative standard deviation (RSD) of 1.0 to 3.3% and sampling rate of 106 h^-1 . The methodology was satisfactorily used to quantify PG-HCl in pharmaceutical tablets with recoveries ranging from 93.17 to 102.77 and RSD from 1.9 to 2.8%.

Flexible membrane composite based on sepiolite/chitosan/(silver nanoparticles) for enrichment and surface-enhanced Raman scattering determination of sulfamethoxazole in animal-derived food

A sepiolite/chitosan/silver nanoparticles (Sep/CTs/AgNPs) membrane substrate has been developed for the fast separation, enrichment, and surface-enhanced Raman scattering (SERS) determination of sulfamethoxazole all-in-one. The Sep/CTs/AgNPs membrane substrate possessed the ability of rapid separation and enrichment to simplify the process for pretreatment and improve the efficiency of analysis. The grown AgNPs can provide abundant hot spots and plasmonic areas to amplify the Raman signals of target molecules effectively. The membrane substrate exhibited good stability with relative standard deviations of 5.8% and 7.1% to same batch and different batches membrane substrate, respectively,  by detecting sulfamethoxazole. The SERS method based on Sep/CTs/AgNPs membrane substrate was used for the determination of sulfamethoxazole with a linear range of 0.05-2.0 mg/L, and the limit of detection was 0.020 mg/L. The established SERS method was finally applied to the quantification of sulfamethoxazole in animal-derived food samples. Sulfamethoxazole was actually found in crucian sample with 12.4 μg/kg, and the result was confirmed by a high-performance liquid chromatography method with relative error of 5.3%. The whole process of analysis can be finished within 25 min with recoveries of 89.3-102.2%. The SERS method based on Sep/CTs/AgNPs membrane substrate provided an integrated strategy for rapid and accurate SERS analysis in food safety issues.

Enhanced ethopabate adsorption in monodispersed porous carbon derived from zeolitic imidazolate framework-8

Drastically improved adsorption capacity for ethopabate is achieved by the partial carbonization of ZIF-8.