Sensitive detection of Ochratoxin A in food and drinks using metal-enhanced fluorescence

An enhanced fluorescent sensor system based on molecularly imprinted polymer chips with silver nanoparticles for highly-sensitive zearalenone analysis

A novel enhanced fluorescent sensor system for zearalenone (ZON) determination in flour samples is presented. The ZON-selective molecularly imprinted polymer (MIP) films were developed with a computational modelling method and synthesised with cyclododecyl-2,4-dihydroxybenzoate as a "dummy" template and ethylene glycol methacrylate phosphate as a functional monomer acted as the selective recognition elements for ZON fluorescence detection. Spherical silver nanoparticles (AgNPs) were embedded in the MIP films' structure to enhance the sensor sensitivity. The imprinted films showed a high ZON recognition ability compared to non-imprinted films. Various factors that affected the measurement of the analysed sample were investigated and optimised. Embedding the AgNPs in the MIP films' structure led to an enhanced sensitivity (up to a 200-fold decrease of LOD) compared to unmodified MIP films. This fluorescent sensor system provided ZON analysis with high sensitivity, specificity, and a wider linear dynamic range of 5 ng mL^-1 to 25 μg mL^-1. An enhanced fluorescent sensor system based on MIP chips with embedded AgNPs could detect trace amounts of ZON in foods and feedstuffs with high sensitivity and selectivity.

Electrochemiluminescence Aptasensor Based on Gd(OH)3 Nanocrystalline for Ochratoxin A Detection in Food Samples

In the present study, the electrochemiluminescence (ECL) properties of Gd(OH)₃ nanocrystals with K₂S₂O₈ as the cathode coreactant were studied for the first time. Based on the prominent ECL behavior of this material and the excellent specificity of the aptamer technique, an ECL aptasensor for the detection of ochratoxin A (OTA) was formulated successfully. Over an OTA concentration range of 0.01 pg mL^-1 to 10 ng mL^-1, the change in the ECL signal was highly linear with the OTA concentration, and the limit of detection (LOD) was 0.0027 pg mL^-1. Finally, the ECL aptasensor was further used to detect OTA in real samples (grapes and corn) and satisfactory results were obtained, which indicated that the built method is expected to be applied in food detection.

[Surface-enhanced Raman detection of deoxynivalenol allenol in agricultural products]

Fungal toxins are secondary metabolites of fungi. Food is highly susceptible to contamination by various fungal species that produce fungal toxins during production and storage. Fungal toxins can cause either acute or chronic poisoning from long-term, low-dose ingestion. Therefore, fungal toxins have become a topic of international interest as a food safety issue. Deoxynivalenol (DON) is a single-terminal sporam toxin produced predominantly by Fusarium graminae and Fusarium pinkosa. DON is globally one of the most common fungal toxins contaminating grain, food, and feed. Various methods have been applied for screening and detecting DON; however, these methods utilize expensive instruments and entail complex operations, poor repeatability, and low sensitivity. Therefore, the development of a simpler, more rapid, and sensitive sensing technology for DON detection is important for applications within the agriculture and food industry. Recently, surface-enhanced Raman scattering (SERS) has become a rapidly developing spectral analysis technology with unique advantages, including high sensitivity, high throughput, and rapid response rates. Therefore, attempts have been made to apply the SERS technique to detecting DON. However, due to the limitations concerning SERS substrates, the currently established SERS method exhibits serious problems, including low sensitivity and weak anti-interference ability, and cannot meet the requirements of sample detection. Recently, our group has prepared aggregated silver nanoparticles (a-AgNPs/CDs) with high SERS activity by using single-layer carbon-based dots (CDs) as a capping agent. Moreover, the obtained materials (a-AgNPs/CDs) were combined with hydrogel technology to prepare novel hydrogel SERS chips. The obtained SERS chips exhibited several advantages over traditional SERS substrates, such as high sensitivity, long-term stability, improved uniformity, and strong anti-interference capabilities. Herein, a novel SERS method for rapid screening and detection of DON in grains was established using a portable Raman spectrometer based on the developed hydrogel SERS chips. The main experimental conditions were optimized before the SERS detection of DON; this included the optimization of the hydrogel SERS chip soaking temperature and time in the DON solution. It was found that the optimal soaking temperature and time were 40 ℃ and 5 min, respectively. Under the optimal SERS detection conditions, the linear response range of DON was 1-10000 μg/kg (correlation coefficient (R2)=0.9967), and the limit of detection (LOD) was 0.14 μg/kg. Due to the unique pore size structure of the hydrogel, common sugar, protein, oil, pigment, and other interfering substances in the sample matrix were blocked outside the hydrogel. Therefore, only simple extraction was required while detecting complex samples. This method was applied to detecting DON in wheat flour, yielding recoveries of 97.3%-103% with relative standard deviations of 4.2%-5.0%. The established SERS method for DON detection exhibits a broader response range, high sensitivity, good repeatability, rapid response, simple operation, and strong anti-interference capability. This shows that the laboratory-constructed hydrogel SERS chip has excellent potential for rapid screening and detection of biotoxins in food.

Highly-selective and sensitive plasmon-enhanced fluorescence sensor of aflatoxins

We demonstrate a novel sensor platform with enhanced sensitivity and selectivity for detecting aflatoxin B1 - a common food toxin in cereals. The approach is based on a molecularly imprinted polymer film that provides selective binding of the aflatoxin B1 and fluorescence signal from the analyte molecule enhanced by the local electric field induced in close proximity to the surface of a silver nanoparticle excited at the localized surface plasmon resonance (LSPR) wavelength. Molecularly imprinted polymers (MIPs) with supramolecular aflatoxin-selective receptor sites and embedded spherical silver nanoparticles (with diameters 30-70 nm, the LSPR band 407 nm) were prepared in the form of a thin polymer film on the surface of a glass slide using in situ polymerization. The detection limit of the sensor for aflatoxin B1 is 0.3 ng mL^-1, which is significantly lower than for a fluorescent sensor without silver nanoparticles. The plasmon-enhanced fluorescence factor is 33, and the linear dynamic range of the sensor is 0.3-25 ng mL^-1.

Fluorescence Enhancement on Silver-Plated Plasma Micro-Nanostructured 3D Polymeric Microarray Substrates for Multiplex Mycotoxin Detection

Oxygen plasma micro-nanostructured poly(methyl methacrylate) (PMMA) slides were modified through silver microparticle deposition to create microarray substrates that enhance the emitted fluorescence intensity. Silver deposition relied on a commercially available reagent and was completed in two 30-min incubation cycles of the substrate with the reagent. The fluorescence enhancement achieved using these substrates over flat PMMA slides was determined through the development of a microarray for the multiplexed detection of four mycotoxins, aflatoxin B1, ochratoxin A, fumonisin B1, and deoxynivalenol. It was shown that the implementation of silver-plated oxygen plasma micro-nanotextured PMMA substrates increased the signals obtained for aflatoxin B1 and ochratoxin A by approximately 2.8 times, 5.6 times for deoxynivalenol, and 16-times for fumonisin B1, compared to flat PMMA substrates. Most notably, this signal increase was not accompanied by a significant increase in the non-specific signal. In addition, the spot repeatability both across a single slide as well as between different slides was high, with coefficients of variation lower than 12%. The slides were also stable for at least three months, thus offering a microarray substrate with improved properties compared to standard glass slides, regarding both the absolute spot fluorescence intensity and between spots repeatability.

Review: Applications of surface-enhanced fluorescence (SEF) spectroscopy in bio-detection and biosensing

Surface-enhanced fluorescence (SEF) is rapidly becoming one of the main spectroscopic techniques for the detection of a variety of biomolecules and biomarkers. The main reasons for this trend are the high sensitivity and selectivity, robustness, and speed of this analytical method. Each year, the number of applications that utilize this phenomenon increases and with each such work, the complexity and novelty of the used substrates, procedures, and analytes rises. To obtain a clearer view of this phenomenon and research area, we decided to combine 76 valuable research articles from a variety of different research groups into this mini-review. We present and describe these works concisely and clearly, with a particular interest in the quantitative parameters of the experiment. These sources are classified according to the nature of the analyte, on the contrary to most reviews, which sort them by substrate nature. This point of view gives us insight into the development of this research area and the consequent increase in the complexity of the analyte nature. Moreover, this type of sorting can show possible future routes for the expansion of this research area. Along with the analytes, we can also pay attention to the substrates used for each situation and how the development of substrates affects the direction of research and subsequently, the choice of an analyte. About 108 sources and several interesting trends in the SEF research area over the past 25 years are discussed in this mini-review.

Detection of mycotoxins and toxigenic fungi in cereal grains using vibrational spectroscopic techniques: a review

Nutrition-rich cereal grains and oil seeds are the major sources of food and feed for human and livestock, respectively. Infected by fungi and contaminated with mycotoxins are serious problems worldwide for cereals and oil seeds before and after harvest. The growth and development activities of fungi consume seed nutrients and destroy seed structures, leading to dramatic declines of crop yield and quality. In addition, the toxic secondary metabolites produced by these fungi pose a well-known threat to both human and animals. The existence of fungi and mycotoxins has been a redoubtable problem worldwide for decades but tends to be a severe food safety issue in developing countries and regions, such as China and Africa. Detection of fungal infection at an early stage and of mycotoxin contaminants, even at a small amount, is of great significance to prevent harmful toxins from entering the food supply chains worldwide. This review focuses on the recent advancements in utilising infrared spectroscopy, Raman spectroscopy, and hyperspectral imaging to detect fungal infections and mycotoxin contaminants in cereals and oil seeds worldwide, with an emphasis on recent progress in China. Brief introduction of principles, and corresponding shortcomings, as well as latest advances of each technique, are also being presented herein.

Assessment of Toxic Effects of Ochratoxin A in Human Embryonic Stem Cells

Ochratoxin A (OTA) is a mycotoxin produced by different Aspergillus and Penicillium species, and it is considered a common contaminant in food and animal feed worldwide. On the other hand, human embryonic stem cells (hESCs) have been suggested as a valuable model for evaluating drug embryotoxicity. In this study, we have evaluated potentially toxic effects of OTA in hESCs. By using in vitro culture techniques, specific cellular markers, and molecular biology procedures, we found that OTA produces mild cytotoxic effects in hESCs by inhibiting cell attachment, survival, and proliferation in a dose-dependent manner. Thus, we suggest that hESCs provide a valuable human and cellular model for toxicological studies regarding preimplantation stage of human fetal development.

Thin Films Sensor Devices for Mycotoxins Detection in Foods: Applications and Challenges

Mycotoxins are a group of secondary metabolites produced by different species of filamentous fungi and pose serious threats to food safety due to their serious human and animal health impacts such as carcinogenic, teratogenic and hepatotoxic effects. Conventional methods for the detection of mycotoxins include gas chromatography and high-performance liquid chromatography coupled with mass spectrometry or other detectors (fluorescence or UV detection), thin layer chromatography and enzyme-linked immunosorbent assay. These techniques are generally straightforward and yield reliable results; however, they are time-consuming, require extensive preparation steps, use large-scale instruments, and consume large amounts of hazardous chemical reagents. Rapid detection of mycotoxins is becoming an increasingly important challenge for the food industry in order to effectively enforce regulations and ensure the safety of food and feed. In this sense, several studies have been done with the aim of developing strategies to detect mycotoxins using sensing devices that have high sensitivity and specificity, fast analysis, low cost and portability. The latter include the use of microarray chips, multiplex lateral flow, Surface Plasmon Resonance, Surface Enhanced Raman Scattering and biosensors using nanoparticles. In this perspective, thin film sensors have recently emerged as a good candidate technique to meet such requirements. This review summarizes the application and challenges of thin film sensor devices for detection of mycotoxins in food matrices.

An optical fiber-based LSPR aptasensor for simple and rapid in-situ detection of ochratoxin A

Label-free biosensing methods that rely on the use of localized surface plasmon resonance (LSPR) have attracted great attention as a result of their simplicity, high sensitivity, and relatively low cost. However, in-situ analysis of real samples using these techniques has remained challenging because colloidal nanoparticles (NPs) can be unstable at certain levels of pH and salt concentration. Even in the case of a chip-type LSPR sensor that can resolve the instability problem by employing NPs immobilized on the substrate, loading of a sample to sensor chip with exact volume control can be difficult for unskilled users. Herein, we report an optical-fiber-based LSPR aptasensor that can avoid these problems and serve as a portable and simple system for sensitive detection of a small mycotoxin, ochratoxin A (OTA), in real samples. The optical fiber coated with aptamer-modified gold nanorods (GNRs) is simply dipped into a solution containing OTA and subjected to LSPR analysis. Quantitative analysis of OTA is performed by measuring the spectral red shift of the LSPR peak of GNRs. Under optimized conditions, the LSPR peak shift displays a linear response (R² = 0.9887) to OTA in the concentration range from 10pM to 100nM, with a limit of detection of 12.0pM (3S). The developed sensor shows a high selectivity for OTA over other mycotoxins such as zearalenone (ZEN) and ochratoxin B (OTB), and shows an accurate detection capability for OTA in real grape juice samples.

A novel single-fluorophore-based ratiometric fluorescent probe for direct detection of isocyanates in air

Airborne isocyanates were conveniently detected by a test paper loaded with a novel single fluorophore ratiometric fluorescent probe.

Ochratoxin A: 50 Years of Research

Since ochratoxin A (OTA) was discovered, it has been ubiquitous as a natural contaminant of moldy food and feed. The multiple toxic effects of OTA are a real threat for human beings and animal health. For example, OTA can cause porcine nephropathy but can also damage poultries. Humans exposed to OTA can develop (notably by inhalation in the development of acute renal failure within 24 h) a range of chronic disorders such as upper urothelial carcinoma. OTA plays the main role in the pathogenesis of some renal diseases including Balkan endemic nephropathy, kidney tumors occurring in certain endemic regions of the Balkan Peninsula, and chronic interstitial nephropathy occurring in Northern African countries and likely in other parts of the world. OTA leads to DNA adduct formation, which is known for its genotoxicity and carcinogenicity. The present article discusses how renal carcinogenicity and nephrotoxicity cause both oxidative stress and direct genotoxicity. Careful analyses of the data show that OTA carcinogenic effects are due to combined direct and indirect mechanisms (e.g., genotoxicity, oxidative stress, epigenetic factors). Altogether this provides strong evidence that OTA carcinogenicity can also occur in humans.

Multiplex surface plasmon resonance biosensing and its transferability towards imaging nanoplasmonics for detection of mycotoxins in barley

A 6-plex mycotoxin assay was developed on a portable nanostructured iSPR and compared with a benchmark double 3-plex SPR assay.

Analytical methods for determination of mycotoxins: An update (2009-2014)

Mycotoxins are a problematic and toxic group of small organic molecules that are produced as secondary metabolites by several fungal species that colonise crops. They lead to contamination at both the field and postharvest stages of food production with a considerable range of foodstuffs affected, from coffee and cereals, to dried fruit and spices. With wide ranging structural diversity of mycotoxins, severe toxic effects caused by these molecules and their high chemical stability the requirement for robust and effective detection methods is clear. This paper builds on our previous review and summarises the most recent advances in this field, in the years 2009-2014 inclusive. This review summarises traditional methods such as chromatographic and immunochemical techniques, as well as newer approaches such as biosensors, and optical techniques which are becoming more prevalent. A section on sampling and sample treatment has been prepared to highlight the importance of this step in the analytical methods. We close with a look at emerging technologies that will bring effective and rapid analysis out of the laboratory and into the field.

Developments in mycotoxin analysis: an update for 2013-2014

This review highlights developments in the determination of mycotoxins over a period between mid-2013 and mid-2014. It continues in the format of the previous articles of this series, emphasising on analytical methods to determine aflatoxins, Alternaria toxins, ergot alkaloids, fumonisins, ochratoxins, patulin, trichothecenes and zearalenone. The importance of proper sampling and sample preparation is briefly addressed in a dedicated section, while another chapter summarises new methods used to analyse botanicals and spices. As LC-MS/MS instruments are becoming more and more widespread in the determination of multiple classes of mycotoxins, another section is focusing on such newly developed multi-mycotoxin methods. While the wealth of published methods during the 12 month time span makes it impossible to cover every single one, this exhaustive review nevertheless aims to address and briefly discuss the most important developments and trends.