Gold nanoparticles as colorimetric probes in food analysis: Progress and challenges

Recent advances in ratiometric electrochemical sensors for food analysis

Ratiometric electrochemical sensors are renowned for their dual-signal processing capabilities, enabling automatic correction of background noise and interferences through built-in calibration, thus providing more accurate and reproducible measurements. This characteristic makes them highly promising for food analysis. This review comprehensively summarizes and discusses the latest advancements in ratiometric electrochemical sensors and their applications in food analysis, emphasizing their design strategies, detection capabilities, and practical uses. Initially, we explore the construction and design strategies of these sensors. We then review the detection of various food-related analytes, including nutrients, additives, metal ions, pharmaceutical and pesticide residues, biotoxins, and pathogens. The review also briefly explores the challenges faced by ratiometric electrochemical sensors in food testing and potential future directions for development. It aims to provide researchers with a clear introduction and serve as a reference for the design and application of new, efficient ratiometric electrochemical sensors in food analysis.

Sensitive colorimetric detection of Vibrio vulnificus based on target-induced shielding against the peroxidase-mimicking activity of CeO2@PtRu nanozyme

Vibrio vulnificus infection caused by contaminated aquatic products and seawater can lead to severe disease and high mortality. The development of a rapid and sensitive detection method for Vibrio vulnificus is vital to effectively prevent infection in advance. In this study, CeO2@PtRu with high peroxidase activity was used to construct a colorimetric immunoassay for Vibrio vulnificus detection by conjugating polyclonal antibodies via the biotin-streptavidin system. The developed colorimetric biosensor for Vibrio vulnificus demonstrated rapid operability and good sensitivity with a detection range from 104 CFU/mL to 109 CFU/mL, and the limit of detection (LOD) is 193 CFU/mL. Moreover, the colorimetric biosensor showed excellent specificity and good recoveries from 98.70% to 102.10% with RSD < 7.45% for spiked real samples. This novel CeO2@PtRu-based colorimetric biosensor has great application potential for the sensitive detection of Vibrio vulnificus in seafood.

Plasmonic colorimetry and G-quadruplex fluorescence-based aptasensor: A dual-mode, protein-free and label-free detection for OTA

G-quadruplexes (G4) have received significant attention in the field of aptasensors owing to their unique physicochemical characteristics. A dual-mode, protein-free and label-free aptamer sensor based on plasmonic colorimetry and G4 fluorescence (PC@GF-aptasensor) was proposed for ochratoxin A (OTA). Colorimetry mode was achieved through the surface plasmon resonance (SPR) effect, which related to the OTA-Apt-based G4-OTA. The fluorescence mode was reflected by the insertion of thioflavin T (ThT) into G4-OTA. The OTA could be interpreted via three readouts: (1) naked eye (LOD of 2.0 ng mL-1), (2) smartphone (LOD of 1.65 ng mL-1), and (3) spectrofluorometer (LOD of 0.93 ng mL-1). The PC@GF-aptasensor exhibited several advantages, such as a standardised recognition group, simplified operation, low background signal, and practicality. The proposed PC@GF-aptasensor integrated SPR-based multicolour interpretation and ThT-inserted fluorescence reflection to obtain a dual-mode optical biosensor, which may provide valuable insights for the development of other targets with G4-based aptamers.

A facile dual-mode SERS/fluorescence aptasensor for AFB1 detection based on gold nanoparticles and magnetic nanoparticles

Aflatoxin B1 (AFB1) is a virulent metabolite secreted by Aspergillus fungi, impacting crop quality and posing health risks to human. Herein, a dual-mode Raman/fluorescence aptasensor was constructed to detect AFB1. The aptasensor was assembled by gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs), while the surface-enhanced Raman scattering (SERS) and fluorescence resonance energy transfer (FRET) effects were both realized. AuNPs were modified with the Raman signal molecule 4-MBA and the complementary chain of AFB1 aptamer (cDNA). MNPs were modified with the fluorescence signal molecule Cy5 and the AFB1 aptamer (AFB1 apt). Through base pairing, AuNPs aggregated on the surface of MNPs, forming a satellite-like nanocomposite, boosting SERS signal via increased "hot spots" but reducing fluorescence signal due to the proximity of AuNPs to Cy5. Upon exposure to AFB1, AFB1 apt specifically bound to AFB1, causing AuNPs detachment from MNPs, weakening the SERS signal while restoring the fluorescence signal. AFB1 concentration displayed a good linear relationship with SERS/fluorescence signal in the range of 0.01 ng/mL-100 ng/mL, with a detection limit as low as 5.81 pg/mL. The use of aptamer assured the high selectivity toward AFB1. Furthermore, the spiked recovery in peanut samples ranged from 91.4 % to 95.6 %, indicating the applicability of real sample detection. Compared to single-signal sensor, this dual-signal sensor exhibited enhanced accuracy, robust anti-interference capability, and increased flexibility, promising for toxin detection in food safety applications.

Nanoparticles for efficient drug delivery and drug resistance in glioma: New perspectives

Gliomas are the most common primary tumors of the central nervous system, with glioblastoma multiforme (GBM) having the highest incidence, and their therapeutic efficacy depends primarily on the extent of surgical resection and the efficacy of postoperative chemotherapy. The role of the intracranial blood-brain barrier and the occurrence of the drug-resistant gene O6-methylguanine-DNA methyltransferase have greatly limited the efficacy of chemotherapeutic agents in patients with GBM and made it difficult to achieve the expected clinical response. In recent years, the rapid development of nanotechnology has brought new hope for the treatment of tumors. Nanoparticles (NPs) have shown great potential in tumor therapy due to their unique properties such as light, heat, electromagnetic effects, and passive targeting. Furthermore, NPs can effectively load chemotherapeutic drugs, significantly reduce the side effects of chemotherapeutic drugs, and improve chemotherapeutic efficacy, showing great potential in the chemotherapy of glioma. In this article, we reviewed the mechanisms of glioma drug resistance, the physicochemical properties of NPs, and recent advances in NPs in glioma chemotherapy resistance. We aimed to provide new perspectives on the clinical treatment of glioma.

A CRISPR/Cas12 trans-cleavage reporter enabling label-free colorimetric detection of SARS-CoV-2 and its variants

We present a label-free colorimetric CRISPR/Cas-based method enabling affordable molecular diagnostics for SARS-CoV-2. This technique utilizes 3,3'-diethylthiadicarbocyanine iodide (DISC2(5)) which exhibits a distinct color transition from purple to blue when it forms dimers by inserting into the duplex of the thymidine adenine (TA) repeat sequence. Loop-mediated isothermal amplification (LAMP) or recombinase polymerase amplification (RPA) was used to amplify target samples, which were subsequently subjected to the CRISPR/Cas12a system. The target amplicons would activate Cas12a to degrade nearby TA repeat sequences, preserving DISC2(5) in its free form to display purple as opposed to blue in the absence of the target. Based on this design approach, SARS-CoV-2 RNA was colorimetrically detected very sensitively down to 2 copies/μL, and delta and omicron variants of SARS-CoV-2 were also successfully identified. The practical diagnostic utility of this method was further validated by reliably identifying 179 clinical samples including 20 variant samples with 100% clinical sensitivity and specificity. This technique has the potential to become a promising CRISPR-based colorimetric platform for molecular diagnostics of a wide range of target pathogens.

Pb2+ Ion Sensors Employing Gold Etching Process: Comparative Investigation on Au Nanorods and Au Nanotriangles

The leaching phenomenon of gold (Au) nanomaterials by Pb2+ ions in the presence of 2-mercaptoethanol (2-ME) and thiosulfate (S2O32- ion) has been systematically applied to a Pb2+ ion sensor. To further investigate the role of Pb2+ ions in sensors containing Au nanomaterials, we revisited the leaching conditions for Au nanorods and compared them with the results for Au nanotriangles. By monitoring the etching rate, it was revealed that Pb2+ ions were important for the acceleration of the etching rate mainly driven by 2-ME and S2O32- pairs, and nanomolar detection of Pb2+ ions were shown to be promoted through this catalytic effect. Using the etchant, the overall size of the Au nanorods decreased but showed an unusual red-shift in UV-Vis spectrum indicating increase of aspect ratio. Indeed, the length of Au nanorods decreased by 9.4% with the width decreasing by 17.4% over a 30-min reaction time. On the other hand, the Au nanotriangles with both flat sides surrounded mostly by dense Au{111} planes showed ordinary blue-shift in UV-Vis spectrum as the length of one side was reduced by 21.3%. By observing the changes in the two types of Au nanomaterials, we inferred that there was facet-dependent alloy formation with lead, and this difference resulted in Au nanotriangles showing good sensitivity, but lower detection limits compared to the Au nanorods.

Plastic probe electrospray ionization mass spectrometry developed for rapid fingerprint profile of biological samples without pretreatment

A triangular-shaped flat plastic substrate probe was prepared for direct electrospray ionization mass spectrometry (ESI-MS) for analysis of untreated chemical and biological samples including liquids (Met-Arg-Phe-Ala peptide, reserpine, and dodecyl aldehyde), solids (biological samples, traditional Chinese medicine), and powders (roasted coffee, rhizoma coptidis, lotus plumule, and Schisandra sphenanthera). Quantitative analysis of reserpine in water yielded a detection limit of 1 ng mL-1, dynamic response range within 1-500 ng mL-1, and linearity of signal response ˃0.9925. Compared to the conventional capillary ESI, this plastic probe ESI offers lower cost of analysis (US $0.0056 per probe), higher sensitivity, lower sample consumption, longer signal duration (>6 min), better reproducibility, signal stability, and higher speed of analysis (<10 s per sample, including sample loading). Overall, the results indicate the potential of ESI-MS based on flat plastic probes as a versatile method for simple, sensitive, and stable analysis of untreated biological sample analysis.

Recent advancements in nanomaterial based optical detection of food additives: a review

Food additives have become a critical component in the food industry. They are employed as preservatives to decelerate the negative effects of environmental and microbial factors on food quality. Currently, food additives are used for a variety of purposes, including colorants, flavor enhancers, nutritional supplements, etc., owing to improvements in the food industry. Since the usage of food additives has increased dramatically, the efficient monitoring of their acceptable levels in food products is quite necessary to mitigate the problems associated with their inappropriate use. The traditional methods used for detecting food additives are generally based on standard spectroscopic and chromatographic techniques. However, these analytical techniques are limited by their high instrumentation cost and time-consuming procedures. The emerging field of nanotechnology has enabled the development of highly sensitive and specific sensors to analyze food additives in a rapid manner. The current article emphasizes the need to detect various food additives owing to their potential negative effects on humans, animals, and the environment. In this article, the role of nanomaterials in the optical sensing of food additives has been discussed owing to their high accuracy, ease-of-use, and excellent sensitivity. The applications of nanosensors for the detection of various food additives have been elaborated with examples. The current article will assist policymakers in developing new rules and regulations to mitigate the adverse effects of toxic food additives on humans and the environment. In addition, the prospects of nanosensors for the optical detection of food additives at a commercial scale have been discussed to combat their irrational use in the food industry.