Recent progress in application of nanomaterial-enabled biosensors for ochratoxin A detection

Highlights

• An overview on current progress in nanomaterial-based ochratoxin A biosensors.

• Optical, electrochemical, and piezoelectric biosensors were mainly discussed.

• Summarized several strategies, i.e. one-step analysis, label-free, and regent-free.

• Major challenges and future perspectives were summarized up.

Abstract

Ochratoxins are the major components of mycotoxin that exist extensively in plant origin food. In the ochratoxins group, ochratoxin A (OTA) as the most toxic compound, which possesses a high chemical and thermal stability in foodstuff and would do harm to human beings. Hence, it is imperative to develop a simple, rapid, sensitive, robust, and accurate way to determine OTA. Nanomaterial-based biosensors seem to be ideal analysis tools for identifying OTA on account of their tremendous merits, such as high sensitivity, excellent selectivity, simplicity of operation, and rapidity. This review focuses on the application and development of nanomaterial-enabled biosensors in OTA detection in the past years (2007–2018). Three dominant signal transduction mechanisms, i.e. optical, electrochemical, and piezoelectric, are discussed in details. Moreover, the major challenges and perspectives for future developments of OTA biosensors are also contained to provide an overview for the forthcoming research orientation.

Introduction

Ochratoxin A (OTA), as a key component of mycotoxin [1], derives from the species of fungi including Aspergillus carbonarius, Penicillium verrucosum, Aspergillus ochraceus, and Aspergillus niger [2], which is supposed to be the most toxic and prevalent toxin existing in an extensive variety of products, such as dried fruits, cereals, nuts, corn, oats, coffee, grape juice, wheat, beer, coffee beans, and wines [3], [4], [5]. OTA is found to cause severely adverse effects including teratogenic, embryotoxic, genotoxic, neurotoxic, immunosuppressive, carcinogenic, and nephrotoxic on humans [6], [7]. In addition, its high chemical stability towards hydrolysis and heat treatments during food processing makes it the most hazardous poison for human. Hence, OTA is classified as possibly carcinogenic to humans (Group 2B) by the International Agency for Research on Cancer [8]. Since the extreme toxicity and common occurrence of OTA, the European Food Safety Authority (EFSA) has conducted the detailed risk assessments for OTA and established the maximum allowable levels presented in food and feed products as well as in raw materials (10 g kg⁻¹ in dried vine fruits and instant coffee, 5 g kg⁻¹ in roasted coffee and raw cereal grains, 3 g kg⁻¹ in processed cereal foods, and 2 g kg⁻¹ in grape juice and all types of wine) [9].

Under these contexts, it is urgently and extremely important to determine OTA levels in contaminated commodities and foodstuffs. In the past decades, diverse analytical means have been constructed for quantitative analysis of OTA. The chromatographic methods, including thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), coupled to ultraviolet visible (UV–Vis), mass spectrometry (MS), or fluorescence detectors [10], [11], [12], [13], [14], [15], [16], [17], are the gold principles to strictly control OTA levels in food samples. These methods may obtain accurate and sensitive results, whereas, tedious sample pretreatment and highly trained personnel are required. Moreover, expensive and sophisticated instruments also restrict these chromatographic methods to in-situ application for OTA detection. Therefore, more convenient, sensitive, and robust methods are still highly desirable for OTA monitoring in foodstuffs.

A biosensor is a device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, organelles, tissues, or whole cells to detect chemical compounds, usually by thermal, electrical, or optical signals [18]. On account of its high sensitivity, excellent selectivity, diverse signal-transducing mechanisms (electrochemical, optical, piezoelectric, etc.), small compact design, and easy operation, biosensor has been extensively studied to quickly acquire to biological or chemical information in the field of environmental monitoring [19], [20], [21], clinical diagnosis [22], [23], [24], and food safety [1], [25]. Particularly, the low-cost feature of biosensor has driven great efforts to develop various biosensors for routine sensing applications in poor regions of the planet. Over the past decade, people have witnessed the great progress and potential of biosensors as appropriate succedaneous or complementary analysis tools for identifying OTA levels in various food samples, such as beverages (red wine, white wine, white grape wine, beer, grape juice, apple juice, milk, etc.) and agricultural products (corn, rice, wheat, peanut, oat, soybean, coffee, apple, etc.). The sample prepare method is diversified. For agricultural products, the pretreatment usually starts with extraction in aqueous-organic solvents (e.g. water-methanol, or water-acetonitrile) or in organic solvents (e.g. chloroform, hexane-acetonitrile, dichloromethane-ethanol, or ethyl acetate), containing additives like sodium hydrogen carbonate or magnesium chloride to enhance solubility and extraction efficiency of OTA [26]. As for beverages, the pretreatment process usually simple, generally following two operations including filtering and dilution [27].

Nanomaterials have been extensively employed for the establishment of biosensors due to their remarkable optical, electronic, thermal, and mechanical properties [28], [29]. Their size related properties, such as high surface area to volume ratio, superior electrical conductivity, magnetic property, and unique physicochemical features [30], [31], have promoted the usage of nanomaterials as catalytic tools, optical or electroactive labels, and immobilization platforms to enhance the biosensing performance to gain higher sensitivity, stability, and selectivity [25], [32]. In recent years, zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) nanomaterials including metal nanomaterials, carbon nanomaterials, up-conversion nanoparticles (UCNPs), magnetic nanoparticles (MNPs), and quantum dots (QDs) have been successfully provided to construct multitudinous biosensors for OTA measurement with increased performance and testing efficiency [5], [33]. Herein, we summarize the current progress and application of nanomaterial-based biosensors for OTA determination (Table 1), aiming to provide the readers an insight into the state-of-art of nanomaterial-based OTA biosensors and expecting to exploit more mature biosensing techniques serving for human beings.