Sensing at nanostructures for agri-food and enviromental applications

With a predicted population increase of 2.3 billion people, by 2050, agricultural productivity must be vastly improved and made sustainable. Globally, agriculture must deliver a 60% increase in food production to cope with the population demand. Moreover, this needs to be achieved against a changing climate, an exploitation of natural resources, and growing water and land scarcities. New digital technologies can optimise production efficiency and ensure food security and safety while also minimising waste within the production systems and the supply chain. To this end, new sensor technologies are being developed for applications in animal health diagnostics and environmental issues related to the global population, such as food & crop protection, pathogen and toxin detection, and environmental remediation. In this thesis, two new nanosensing diagnostic devices are developed and presented; surface enhanced Raman sensing and electrochemical sensing. Surface-enhanced Raman spectroscopy (SERS) substrates were fabricated by templating a flexible thermoplastic polymer against an aluminium drinks can followed by coating with a silver film, to produce a rough nanostructured metallic surface. SERS is used for both qualitative (molecular fingerprint) and quantitative detection of dye molecules and food toxins. In addition, the SERS technique is also applied in combination with nanoelectrochemical square wave voltammetry to detect nano-concentrations of neonicotinoid pesticides. The enhanced sensitivity and minimum sample preparation requirements provide tremendous opportunities for food safety and security sectors. An impedimetric immunosensor device (with a micro SD style pin-out) was also developed for the serological diagnosis of viruses and antibodies associated with bovine respiratory disease and bovine liver fluke. The silicon chip devices consist of six on-chip nanoband electrodes which can be independently modified with a polymer layer for covalent immobilisation of capture and target biomolecules. This electrochemical biosensor technology provides label-free and cost-efficient sensing capability in a compact size, and demonstrates the potential development of immunoassay-based point-of-use devices for on-farm diagnosis or therapeutic monitoring in animal health applications

Transparent polymer-based SERS substrates templated by a soda can

This paper demonstrates the reproducible fabrication of transparent Surface Enhanced Raman Scattering (SERS) substrates, fabricated by employing an aluminium soda can to template nanostructures on a flexible thermoplastic polymer surface, followed by deposition of a silver over layer. Electron microscopy and finite element modelling simulations strongly suggested the SERS response arose at regions of high electromagnetic field strength occurring between metallic clusters following illumination by monochromatic radiation. The sensors exhibited rapid, quantitative and high sensitivity, for example, 5 × 10−10 M (204 pg/mL) crystal violet detection in 10 min using a simple drop and dry method. We also show detection of glucose employing a chemically modified silver surface bearing a pre-deposited SAM layer. Furthermore, the transparent substrates permitted back excitation and collection through the substrate with corresponding spectra exhibiting clear and well-defined spectral SERS peaks. Finally, we present the detection of trace amounts of melamine in complex media solution (milk and infant formula). We benchmark the sensor performance using commercial analytical instrumentation (MS-MS) and show comparable sensitivity between the SERS substrates and MS-MS

Direct correlation between potentiometric and impedance biosensing of antibody-antigen interactions using an integrated system

A fully integrated system that combines extended gate field-effect transistor (EGFET)-based potentiometric biosensors and electrochemical impedance spectroscopy (EIS)-based biosensors has been demonstrated. This integrated configuration enables the sequential measurement of the same immunological binding event on the same sensing surface and consequently sheds light on the fundamental origins of sensing signals produced by FET and EIS biosensors, as well as the correlation between the two. Detection of both the bovine serum albumin (BSA)/anti-BSA model system in buffer solution and bovine parainfluenza antibodies in complex blood plasma samples was demonstrated using the integrated biosensors. Comparison of the EGFET and EIS sensor responses reveals similar dynamic ranges, while equivalent circuit modeling of the EIS response shows that the commonly reported total impedance change (DZtotal) is dominated by the change in charge transfer resistance (Rct) rather than surface capacitance (Csurface). Using electrochemical kinetics and the Butler-Volmer equation, we unveil that the surface potential and charge transfer resistance, measured by potentiometric and impedance biosensors, respectively, are, in fact, intrinsically linked. This observation suggests that there is no significant gain in using the FET/EIS integrated system and leads to the demonstration that low-cost EGFET biosensors are sufficient as a detection tool to resolve the charge information of biomolecules for practical sensing applications

Advanced solid state nano-electrochemical sensors and system for agri 4.0 applications

Global food production needs to increase in order to meet the demands of an ever growing global population. As resources are finite, the most feasible way to meet this demand is to minimize losses and improve efficiency. Regular monitoring of factors like animal health, soil and water quality for example, can ensure that the resources are being used to their maximum efficiency. Existing monitoring techniques however have limitations, such as portability, turnaround time and requirement for additional reagents. In this work, we explore the use of micro- and nano-scale electrode devices, for the development of an electrochemical sensing platform to digitalize a wide range of applications within the agri-food sector. With this platform, we demonstrate the direct electrochemical detection of pesticides, specifically clothianidin and imidacloprid, with detection limits of 0.22 ng/mL and 2.14 ng/mL respectively, and nitrates with a detection limit of 0.2 µM. In addition, interdigitated electrode structures also enable an in-situ pH control technique to mitigate pH as an interference and modify analyte response. This technique is applied to the analysis of monochloramine, a common water disinfectant. Concerning biosensing, the sensors are modified with bio-molecular probes for the detection of both bovine viral diarrhea virus species and antibodies, over a range of 1 ng/mL to 10 µg/mL. Finally, a portable analogue front end electronic reader is developed to allow portable sensing, with control and readout undertaken using a smart phone application. Finally, the sensor chip platform is integrated with these electronics to provide a fully functional end-to-end smart sensor system compatible with emerging Agri-Food digital decision support tools

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids

Advanced data acquisition for emerging nano-electrochemical sensors

This paper describes a low cost portable point of test data acquisition system, made of commercial components, that was developed to interface to electrochemical sensors. The proposed system has demonstrated that it can support cyclic voltammetry, square wave voltammetry and collector generator voltammetry, with dual electrode control. The system has demonstrated its capability to detect a range of ferrocene monocarboxylic acid concentrations using nanowire electrochemical sensors, while benchmarking the results against dedicated laboratory based equipment. This work has identified and highlighted the unique challenges of interfacing to electrochemical sensors

Electrochemical-Based Serological Detection of Bovine Immunoglobulin G in Calves

Bovine antibodies, such as immunoglobulin G (IgG), cannot pass the placental barrier and as such are not transferred from the mother to the foetus, in utero. Instead a calf must absorb antibodies following ingestion of colostrum postpartum. Failure of Passive Transfer (FPT) is a condition that predisposes calves to development of disease and increases the risk of mortality. Thus, continuous early monitoring of IgG absorption in a calf, within the first 24 hours of life, is imperative to allow faster treatment and prevent FPT. In this paper, we present the development of a label-free impedimetric immunosensor device for bovine IgG in serum and demonstrate its suitability to determine early FPT in new-born calves. The developed sensors were challenged to discriminate between new born calf sera, both pre- and post-colostrum feeding, and demonstrated efficent detection of IgG in under 15 minutes. Such a device could enable rapid determination of FPT, thereby improving calves’ vitality and survival rat

Label-Free Impedimetric Nanoband Sensor for Detection of Both Bovine Viral Diarrhoea Virus (BVDV) and Antibody (BVDAb) in Serum

In veterinary medicine, diagnostic tools enabling early detection of infectious disease in cattle could play a pivotal role in the control and eradication of bovine viral diarrhoea (BVD). Early identification of cattle persistently infected with bovine viral diarrhoea virus (BVDV) is critical for early diagnosis and isolation of the animal from a susceptible herd. The immediate availability of electronic test results to a veterinarian on-farm, would eliminate the need to submit samples to a commercial laboratory thereby improving animal therapeutic outcomes considerably. An impedimetric silicon chip-based biosensor platform, containing six gold nanoband electrodes as six individual sensors, was developed in this study for detection of BVD disease target molecules. Gold nanoband electrodes were first coated with an electrodeposited polymer and then modified with either monoclonal antibodies or Erns protein, for the subsequent detection of BVD virus and antibodies in whole serum, respectively. We demonstrate that the nanoband sensors have sufficient sensitivity and specificity for serological detection of both targets, with a low time-to-result (20 minutes). All serological samples were benchmarked against, and in complete agreement with, gold standard commercial ELISA methods. These initial proof-of-concept findings are of particular significance for potential on-farm point of use applications, where rapid analysis times and specificity are required to permit early diagnostics by veterinarians. </p