Smartphone-based magneto-immunosensor on carbon black modified screen-printed electrodes for point-of-need detection of aflatoxin B1 in cereals

Considering the complexities and speed of modern food chains, there is an increasing demand for point-of-need detection of food contaminants, particularly highly regulated chemicals and carcinogens such as aflatoxin B1. We report a user-friendly smartphone-based magneto-immunosensor on carbon black modified electrodes for point-of-need detection of aflatoxin B1 in cereals. For buffered analyte solutions and a corn extract sample, the assay demonstrated a low limit of detection of 13 and 24 pg/mL, respectively. The assay was also highly reproducible, exhibiting mean relative standard deviations of 3.7% and 4.0% for the buffered analyte and corn extract samples. The applicability of the assay was validated on the basis of EU guidelines and the detection capability was lower than or equal to 2 μg/kg, which is the EU maximum residue limit for aflatoxin B1 in cereals. False-positive and false-negative rates were less than 5%. Additionally, an open-source android application, AflaESense, was designed to provide a simple interface that displays the result in a traffic-light-type format, thus minimizing user training and time for data analysis. AflaESense was used for smartphone-based screening of spiked corn samples containing aflatoxin B1 (0.1, 2, and 10 ng/mL), and naturally contaminated corn containing 0.15 ng aflatoxin B1/mL. The measured values were in close agreement with spiked concentrations (r2 = 0.99), with recovery values ranging between 80 and 120%. Finally, contaminated samples correctly triggered a red alert while the non-contaminated samples led to the display of a green color of AflaESense. To the best of our knowledge, this is the first smartphone-based electrochemical system effective for screening samples for contamination with aflatoxin B1.We thank Prof. Michel Nielen ((Wageningen Food Safety Research (WFSR), part of Wageningen University & Research, Wageningen, The Netherlands) for kindly providing the certified non-contaminated (blank) and naturally contaminated samples.Peer reviewe

Carbon black modified screen printed electrodes and magnetic beads for mass production compatible point of site detection of domoic acid in shellfish

Carbon screen-printed electrodes (SPEs) are an optimum platform for point-ofsite electrochemical detection due to their low background currents, wide potential window and chemical inertness. Advancements in screen printing technology has pushed the development of these cost-effective sensors across multiple fields. However, sensitivity of SPEs is suboptimal and improvement of SPE based detection has been accomplished by modifying SPEs with drop-casted nanomaterials such as graphene and carbon nanotubes or electrodepositioned gold nanoparticles. Unfortunately, these modifications are costly and/or time consuming and impair price-competitive mass production. Moreover, biofunctionalisation of the modified SPEs further complicates mass production/storage and is known to be sensitive to matrix effects due to washing difficulties. These facts may account, at least in part, for why SPE based sensors are currently not commercially available for food contaminant detection. In the present study novel solutions were sought to enable the creation of a cost effective, mass production compatible and sensitive SPE based biosensor with reduced matrix effects. Carbon black (CB), (a largely unexplored material with similar electocatalytic properties as graphene and carbon nanotubes but at least 100X more cost effective) and synthesized gold nanospheres or gold nanostars (which were simply drop-cast onto the SPE thus avoiding lengthy electrodeposition steps) were used for the modification of homemade SPEs. The electrochemical performance of the nanomaterial-SPEs was compared to SPEs which underwent classic (timeconsuming) pre-anodization in phosphate buffer (Pre-SPEs). A magnetic-bead hapten conjugate was used for the development of a competitive immunoassay based on the Enzyme-Linked-Immunomagnetic-Electrochemical (ELIME) format to allow better washing and avoid SPE biofunctionalisation. Finally, optimized nanomaterial-SPEs and pre-SPEs were used for the detection of the regulated marine toxin, domoic acid (DA), in buffer, spiked shellfish matrix and naturally contaminated shellfish. This comparison showed that CB-SPE had the best performance and enables detection of DA with a LOD tenfold lower as Pre-SPE in buffer (4 ng/ml vs. 0.4 ng/ml). Matrix effects remained limited with a LOD in spiked matrix of 0.7 ng/ml and a final LOD of 0.7 mg DA/kg shellfish (well below the EU action level of 20 mg DA/kg shellfish). Moreover, good agreement with HPLC data for DA quantification in contaminated scallops (R2=0.965) was obtained. In summary, this work led to the identification of the largely unexplored carbon-nanomaterial CB as highly interesting for SPE modification and showcased that combining CB and the ELIME format has merit for the development of a mass production compatible, robust, cost effective (material cost < €1.0 per assay) biosensor for in-situ detection of contaminants in a complex matrix

The benefits of carbon black, gold and magnetic nanomaterials for point-of-harvest electrochemical quantification of domoic acid

Gold nanostars (GNST), gold nanospheres (GNP) and carbon black (CB) are chosen as alternative nanomaterials to modify carbon screen-printed electrodes (c-SPEs). The resulting three kinds of modified c-SPEs (GNP-SPE, CB-SPE and GNSP-SPE) were electrochemically and microscopically characterized and compared with standardized c-SPEs after pretreatment with phosphate buffer by pre-anodization (pre-SPE). The results show outstanding electrochemical performance of the carbon black-modified SPEs which show low transient current, low capacitance and good porosity. A competitive chronoamperometric immunoassay for the shellfish toxin domoic acid (DA) is described. The performances of the CB-SPE, GNP-SPE and pre-SPE were compared. Hapten-functionalized magnetic beads were used to avoid individual c-SPE functionalization with antibody while enhancing the signal by creating optimum surface proximity for electron transfer reactions. This comparison shows that the CB-SPE biosensor operated best at a potential near − 50 mV (vs. Ag/AgCl) and enables DA to be determined with a detection limit that is tenfold lower compared to pre-SPE (4 vs. 0.4 ng mL−1). These results show very good agreement with HPLC data when analysing contaminated scallops, and the LOD is 0.7 mg DA kg−1 of shellfish.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 720325.Peer reviewe

ASSURED Point-of-Need Food Safety Screening: A Critical Assessment of Portable Food Analyzers

Standard methods for chemical food safety testing in official laboratories rely largely on liquid or gas chromatography coupled with mass spectrometry. Although these methods are considered the gold standard for quantitative confirmatory analysis, they require sampling, transferring the samples to a central laboratory to be tested by highly trained personnel, and the use of expensive equipment. Therefore, there is an increasing demand for portable and handheld devices to provide rapid, efficient, and on-site screening of food contaminants. Recent technological advancements in the field include smartphone-based, microfluidic chip-based, and paper-based devices integrated with electrochemical and optical biosensing platforms. Furthermore, the potential application of portable mass spectrometers in food testing might bring the confirmatory analysis from the laboratory to the field in the future. Although such systems open new promising possibilities for portable food testing, few of these devices are commercially available. To understand why barriers remain, portable food analyzers reported in the literature over the last ten years were reviewed. To this end, the analytical performance of these devices and the extent they match the World Health Organization benchmark for diagnostic tests, i.e., the Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users (ASSURED) criteria, was evaluated critically. A five-star scoring system was used to assess their potential to be implemented as food safety testing systems. The main findings highlight the need for concentrated efforts towards combining the best features of different technologies, to bridge technological gaps and meet commercialization requirements