Fabrication of porous ZnO/Co3O4 nanohybrids for the application of surface enhanced Raman scattering

With the growing use of various pesticides, it is important to develop facile and sensitive method to detect pesticides residues in food. Here, a semiconductor/magnetic hybrid material was used as surface enhanced Raman scattering (SERS) substrate to detect simulated residues. The representative sample of porous ZnO/Co₃O₄ nano-cube was fabricated by pyrolysis and calcination of Zn-Co ZIF, successively. The obtained hybrid of ZnO/Co₃O₄ was employed as substrate to detect of crystal violet (CV) and Rhodamine B (Rh B), and showed remarkable SERS performance. The detection limit of Rh B was 1 × 10^-10 M as well as CV of 1 × 10^-9 M. The results indicated that it was an ideal choice to improve the SERS property of transition metal oxide substrates by doping semiconductor. The semiconductor/magnetic hybrid material highlighted the obvious characteristics of low cost, facile preparation and ultra-low detection limit in the SERS measurements. The hybrids with the combination of semiconductor/magnetic properties showed a further widely application and development in SERS detection of pesticides residues.

Functionalized silver nanoparticles for SERS amplification with enhanced reproducibility and for ultrasensitive optical fiber sensing in environmental and biochemical assays

Plasmonic sensors have broad application potential in many fields and are promising to replace most bulky sensors in the future. There are various method-based chemical reduction processes for silver nanoparticle production with flexible structural shapes due to their simplicity and rapidity in nanoparticle fabrication. In this study, self-assembled silver nanoparticles (Ag NPs) with a plasmon peak at 424 nm were successfully coated onto -NH2-functionalized glass and optical fiber sensors. These coatings were rapidly produced via two denaturation reactions in plasma oxygen, respectively, and an APTES ((3-aminopropyl)triethoxysilane) solution was shown to have high strength and uniformity. With the use of Ag NPs for surface-enhanced Raman scattering (SERS), excellent results and good stability with the detection limit up to 10-10 M for rhodamine B and 10-8 M for methylene blue, and a signal degradation of only ∼20% after storing for 30 days were achieved. In addition, the optical fiber sensor with Ag NP coatings exhibited a higher sensitivity value of 250 times than without coatings to the glycerol solution. Therefore, significant enhancement of these ultrasensitive sensors demonstrates promising alternatives to cumbersome tests of dye chemicals and biomolecules without any complicated process.

Rapid and sensitive detection of Rhodamine B in food using the plasmonic silver nanocube-based sensor as SERS active substrate

The use of dye in food is harmful to human health and is prohibited nowadays. However, it is still used because of the benefits, such as cheap prices and abundant resources. Rhodamine B is usually used as the colorant in food such as chili powder, chili oil, etc. It is colorless at very low concentration 10^-7 M. The sensitive detection of RhB at ultra-low concentration help to prevent some risk for human. Surface-enhanced Raman scattering (SERS) is a great technique to detect the analytes at ultra-low concentration and provide the molecule's information as a fingerprint. In this study, silver nano-cube was facilely synthesized by reducing Ag⁺ in ethylene glycol and upgraded to thin-film as a SERS active substrate. RhB was detected at 10^-10 M by a silver nano-cube sensor. The dynamic linear regression between the Raman intensity and RhB concentration over seven orders of magnitude (from 10^-4 to 10^-10 M) was excellent with high reliability (R² = 0.99). Moreover, the substrate can be used after storing in a dark area for 60 days. This proposed nano-cube silver could serve as a potential substrate for detecting RhB in food at very low concentration.

Molecularly Imprinted Polymers (MIPs) in Sensors for Environmental and Biomedical Applications: A Review

Molecular imprinted polymers are custom made materials with specific recognition sites for a target molecule. Their specificity and the variety of materials and physical shapes in which they can be fabricated make them ideal components for sensing platforms. Despite their excellent properties, MIP-based sensors have rarely left the academic laboratory environment. This work presents a comprehensive review of recent reports in the environmental and biomedical fields, with a focus on electrochemical and optical signaling mechanisms. The discussion aims to identify knowledge gaps that hinder the translation of MIP-based technology from research laboratories to commercialization.

An overview on molecular imprinted polymers combined with surface-enhanced Raman spectroscopy chemical sensors toward analytical applications

Surface-enhanced Raman spectroscopy (SERS) is a powerful and high-speed detection technology. It provides information on molecular fingerprint recognition with ultrahigh sensitive detection. However, it shows poor anti-interference capacity against complex matrices. Molecularly imprinted polymers (MIPs) can achieve specific recognition of targets from complex matrices. Through introducing the MIP separation system, the MIP-SERS chemical sensor can effectively overcome the limitation of complex matrix interference, and further improve the stability of sensors for detection. Herein, the materials and structures of integrated MIP-SERS sensors are systematically reviewed, and its application as a sensor for chemical detection of hazardous substances in environmental and food samples has been addressed as well. To broaden the prospects of application, we have discussed the current challenges and future perspectives that would accelerate the development of versatile MIP-SERS chemical sensors.

Molecular-Imprinting-Based Surface-Enhanced Raman Scattering Sensors

Molecularly imprinted polymers (MIPs) receive extensive interest, owing to their structure predictability, recognition specificity, and application universality as well as robustness, simplicity, and inexpensiveness. Surface-enhanced Raman scattering (SERS) is regarded as an ideal optical detection candidate for its unique features of fingerprint recognition, nondestructive property, high sensitivity, and rapidity. Accordingly, MIP based SERS (MIP-SERS) sensors have attracted significant research interest for versatile applications especially in the field of chemo- and bioanalysis, showing excellent identification and detection performances. Herein, we comprehensively review the recent advances in MIP-SERS sensors construction and applications, including sensing principles and signal enhancement mechanisms, focusing on novel construction strategies and representative applications. First, the basic structure of the MIP-SERS sensors is briefly outlined. Second, novel imprinting strategies are highlighted, mainly including multifunctional monomer imprinting, dummy template imprinting, living/controlled radical polymerization, and stimuli-responsive imprinting. Third, typical application of MIP-SERS sensors in chemo/bioanalysis is summarized from both small and macromolecular aspects. Lastly, the challenges and perspectives of the MIP-SERS sensors are proposed, orienting sensitivity improvement and application expanding.

Rapid and sensitive biomarker detection using molecular imprinting polymer hydrogel and surface-enhanced Raman scattering

Biomarkers are important biochemical indicators, which could be used for identification, early diagnosis and monitoring of diseases during the course of treatment. However, biomarker diagnosis has some shortcomings such as requiring a large amount of samples, long test time and high cost, which seriously influences the correctness and timely treatment to patients. Here, a relatively fast and efficient plasmonic hot spot-localized surface imprinting of Ag spheres using biomarker template immobilization and hydrogel copolymerization is described. The technique takes a fine control of the imprinting process at the nanometre scale and provides a biosensor with high sensitivity. Proof of the opinion is established by detection of biomarker using surface-enhanced Raman scattering (SERS) spectroscopy. This work represents a valuable step towards SERS with biomarkers for cost-saving and time-saving diagnostic assay. It is expected that the new surface imprinted hydrogel plasmonic material can drive possibilities in advancing application of biomarkers in plasmonic biosensors.

Preparation of triangular silver nanoplates by silver seeds capped with citrate-CTA+

Due to the competitive growth on the crystal face of seed, it is always difficult to control the morphology of the formation of nanoparticles precisely by a seed-mediated growth method. Herein, we provided a simple but effective technique to synthesize silver nanotriangles using a new silver seed that is capped with citrate-CTA⁺ (CTA⁺ is cetyltrimethyl ammonium cation). Compared to the preparation of silver nanoparticles (AgNPs) by a conventional seed-mediated method, in this paper, we presented a growth technique with two distinct innovative changes. First, the concentrations of CTAB that we added in silver seed collosol have a significant impact on the size distribution, and silver nanotriangles, nanorods, and nanospheres could be obtained by adjusting the CTAB concentration. Second, the seed prepared by our method has a longer use time, and silver nanotriangles, nanospheres, and nanorods could be prepared by adjusting the aged time of the seed colloid. We have also shown a simple way to control the morphology of silver nanoparticles in almost the same reactive medium by varying the NaOH concentration. Using the new silver seed capped with citrate-CTA⁺, we obtained triangular silver nanoparticles with relatively high regularity. Based on the limited experimental results and IR analysis, a possible mechanism was preliminarily proposed to explain the formation of the seed and the truncated triangular AgNPs.

Due to the competitive growth on the crystal face of seed, it is always difficult to control the morphology of the formation of nanoparticles precisely by a seed-mediated growth method.

Molecular imprinting polymers and their composites: a promising material for diverse applications

Molecular imprinted polymerization is considered one of the most useful preparation strategies to obtain highly selective polymeric materials called molecular imprinted polymers (MIPs).