Progress in fluorescence biosensing and food safety towards point-of-detection (PoD) system

The detection of pathogens in food substances is of crucial concern for public health and for the safety of the natural environment. Nanomaterials, with their high sensitivity and selectivity have an edge over conventional organic dyes in fluorescent-based detection methods. Advances in microfluidic technology in biosensors have taken place to meet the user criteria of sensitive, inexpensive, user-friendly, and quick detection. In this review, we have summarized the use of fluorescence-based nanomaterials and the latest research approaches towards integrated biosensors, including microsystems containing fluorescence-based detection, various model systems with nano materials, DNA probes, and antibodies. Paper-based lateral-flow test strips and microchips as well as the most-used trapping components are also reviewed, and the possibility of their performance in portable devices evaluated. We also present a current market-available portable system which was developed for food screening and highlight the future direction for the development of fluorescence-based systems for on-site detection and stratification of common foodborne pathogens

SILVER MIRROR SUBSTRATE AND ROLLING METHOD FOR IMPROVED SURFACE-ENHANCED RAMAN SPESCTROSCOPIC ANALYSIS IN FOOD

Surface-enhanced Raman spectroscopy, short for SERS, is an emerging technology with great potential in food analysis due to rapid detection, high sensitivity, portable instrumentation, and simple sample preparation. However, it is always a bottleneck to obtain reproducible SERS measurements in real analytical cases due to the complicity of food systems and inhomogeneous aggregation of colloidal nanoparticles. To improve its performance for practical applications in food analysis, efforts have been made in improving the reproducibility, enhancing the selectivity and reducing the matrix interference to the analyte. Herein, a self-assembly silver nanoparticles mirror substrate was fabricated to improve the and the quantitative ability and effectiveness of sample preparation for different applications in food analysis, including pesticides detection in beverages, chemical profiling of red wines, and headspace analysis of garlic. The AgNPs mirror was fabricated using the interface between polar and non-polar solvents and showed a uniform arrangement of nanoparticles under the microscope. It demonstrated a great reliability for the detection of a pesticide fonofos in beverages (i.e., apple juice and green tea). AgNPs mirror can also be in situ fabricated in red wines to generate a comprehensive spectrum constituted by signals of five wine phytochemicals, which provided a great potential of SERS in the differentiation, authentication, and quality/safety control of red wines. AgNPs mirror also showed great potential in the headspace characterization of aromatic compounds from Allium species plants. Additionally, a facile rolling method was developed to enrich analyte (i.e., chlordane pesticide) and to amplify its weak SERS activity and a mathematic model was generated and successfully quantified the chlordane in a complicated crude oil sample with a very good recovery. Overall, AgNPs mirror and the rolling method overcame the reproducibility and sensitivity problems for SERS in several challenging food matrices. With these improvements, SERS can be much more reliable for analytical applications and its range of targets can be widely expanded

Cellulose-Based Biosensing Platforms

Cellulose empowers measurement science and technology with a simple, low-cost, and highly transformative analytical platform. This book helps the reader to understand and build an overview of the state of the art in cellulose-based (bio)sensing, particularly in terms of the design, fabrication, and advantageous analytical performance. In addition, wearable, clinical, and environmental applications of cellulose-based (bio)sensors are reported, where novel (nano)materials, architectures, signal enhancement strategies, as well as real-time connectivity and portability play a critical role

Applications of Quantum Dots in the Food Industry

Quantum dots (QDs) are spherical particles with a size of <10 nm and, due to their unique properties, have good potential for use in the food industry. Among the various QDs, food industry researchers have highly regarded carbon quantum dots (CQDs) due to their nontoxicity and environmental friendliness. Food analysis is essential for quality assessment as well as safety control. In this regard, QDs-based fluorescence sensors can provide faster, more accurate, more sensitive, and cheaper analysis methods. The use of QDs to detect food additives, pathogens, heavy metals, nutrients, antibiotics, and insecticide residues is investigated in this chapter. QDs in packaging materials, due to their antioxidant, antimicrobial, and inhibitory properties, increase product shelf life, reduce the growth of microorganisms, improve mechanical properties, prevent gases and UV light, and reduce food waste. Their application in improved, active, intelligent, and bio-packaging will also be described. Then, their application in water treatment will be discussed. QDs, due to properties such as high aspect ratio, reactivity, electrostatic, hydrophilic, and hydrophobic interactions, have good potential for use in various water treatment methods, including membranes in filtration, adsorbents, and photocatalysts. Finally, their use to track protein will be investigated

Biosensors for Environmental Monitoring

Real-time and reliable detection of molecular compounds and bacteria is essential in modern environmental monitoring. For rapid analyses, biosensing devices combining high selectivity of biomolecular recognition and sensitivity of modern signal-detection technologies offer a promising platform. Biosensors allow rapid on-site detection of pollutants and provide potential for better understanding of the environmental processes, including the fate and transport of contaminants.This book, including 12 chapters from 37 authors, introduces different biosensor-based technologies applied for environmental analyses

Κατασκευή και εφαρμογές απορριπτόμενων αισθητήρων για τον ηλεκτροχημικό προσδιορισμό οργανικών ενώσεων

Στο πλαίσιο της παρούσας Διδακτορικής Διατριβής πραγματοποιήθηκε ανάπτυξη ηλεκτροχημικών αισθητήρων εκτύπωσης και μεθόδων και για τον προσδιορισμό ορισμένων σημαντικών οργανικών ενώσεων. Κατασκευάστηκαν εκτυπωμένα ηλεκτρόδια, τροποποιημένα με πρόδρομες ενώσεις του βισμουθίου, για τον προσδιορισμό τριών νιτροφαινολών (2-νιτροφαινόλη, 4-νιτροφαινόλη, 2,4-δινιτροφαινόλη) Αναπτύχθηκε μέθοδος καθοδικής βολταμμετρίας διαφορικού παλμού για τον προσδιορισμό αυτών των νιτροφαινολών σε νερό. Τα όρια ποσοτικοποίησης σε 3 δείγματα νερού ήταν στην περιοχή 1,1-2,2 μmol L-1 ενώ χρησιμοποιώντας εκχύλιση στερεάς φάσης, τα όρια ποσοτικοποίησης κυμάνθηκαν στο εύρος 0,021-0,025 μmol L-1. Η μέση % ανάκτηση σε δείγματα νερού κυμάνθηκε στην περιοχή από 87 έως 108 %. Επίσης, αναπτύχθηκε μέθοδος καθοδικής βολταμμετρίας διαφορικού παλμού για τον προσδιορισμό πέντε νεονικοτινοειδών φυτοφαρμάκων (Imidacloprid, Thiamethoxam, Clothianidin Nitenpyram, Dinotefuran) σε νερό με εκτυπωμένα ηλεκτρόδια, τροποποιημένα με παχύ φιλμ βισμουθίου. Τα όρια ποσοτικοποίησης ήταν από 0,76 έως 2,10 mg L-1 ενώ μετά εκχύλιση στερεάς φάσης ήταν στην περιοχή από 9.0 έως 17 μg L-1, με την ανάκτηση να κυμαίνεται στην περιοχή από 89 έως 109 %. Η τρίτη εφαρμογή αφορά τον προσδιορισμό 4 αζωχρωμάτων (Ponceau 4R-CarmoisineSunset Yellow-Tartrazine) σε μη αλκοολούχα ποτά με εκτυπωμένα ηλεκτρόδια γραφίτη. Τα όρια ανίχνευσης κυμάνθηκαν από 0,02 έως 0,04 mg L-1 και οι ανακτήσεις στα δείγματα ήταν στην περιοχή από 95 έως 109 %. Τέλος, κατασκευάστηκαν εκτυπωμένα ηλεκτρόδια, τροποποιημένα με γραφένιο/Nafion, και αναπτύχθηκε μέθοδος ανοδικής αναδιαλυτικής βολταμμετρία για τον προσδιορισμό καφεΐνης σε τρόφιμα. Το όριο προσδιορισμού ήταν 0,06 μmol L-1 και οι ανακτήσεις κυμάνθηκαν στην περιοχή από 101 έως 106%. Οι εκτυπωμένοι αισθητήρες παρουσιάζουν σχετικά ικανοποιητική ευαισθησία (ιδίως όταν προηγείται στάδιο προκατεργασίας/προσυγκέντρωσης) ενώ το μεγαλύτερο μειονέκτημά τους είναι η μειωμένη εκλεκτικότητα, συνεπώς η εφαρμοσιμότητα τους εξαρτάται από το δείγμα υπό ανάλυση. Οι αισθητήρες είναι κατάλληλοι για γρήγορη ανίχνευση (screening) νιτροφαινολών και νεονικοτινοειδών φυτοφαρμάκων σε νερό, για τον προσδιορισμό μεμονωμένων χρωστικών σε ποτά και για τον προσδιορισμό καφεΐνης σε τρόφιμα.In the present study we have developed and evaluated disposable sensors for the determination of some important organic compounds. Screen-printed disposable sensors modified with bismuth precursors were fabricated and applied for the first time to organic cathodic electroanalysis, namely to the determination of 2-nitrophenol, 4-ntrophenol and 2,4-dnitrophenol, in water samples by differential pulse cathodic voltammetry. The limits of quantification in 3 different water matrices were in the range 1.1-2.2 μmol L-1. Using a simple solid-phase extraction procedure, the limits of quantification were in the range 0.021-0.025 μmol L-1 while the recoveries of samples spiked with the 3 target nitrophenols were between 87 % and 108 %. The applicability of sputtered thick-film bismuth electrodes was tested for the determination of five pesticides (Imidacloprid, Thiamethoxam, Clothianidin, Nitenpyram, Dinotefuran) in different water matrices by differential pulse cathodic voltammetry. The limits of quantification in 4 different water matrices were in the range 0.76 to 2.10 mg L-1. Using a simple solid-phase extraction procedure, the matrix effects were substantially reduced and the limits of quantification were in the range 9.0 to 17 μg L-1, while the recoveries were in the range 89 to 109%. In the third part of this thesis, the application of bare screen-printed electrodes in the voltammetric determination of 4 azo-dyes (Ponceau-4R, Carmoisine, Sunset-Yellow, Tartrazine) in beverages was examined. The limits of detection were in the range 0.02 to 0.04 mg L-1 while the recoveries were in the range 95 to 109%. Finally, screen-printed electrodes modified with graphene/Nafion were fabricated for the determination of caffeine in food samples by anodic adsorptive stripping voltammetry. The limit of quantification was 0.06 μmol L-1, while the recoveries were in the range 101 to 106%. The proposed screen-printed sensors exhibit satisfactory sensitivity (especially when a preconcentration step is included), while their biggest drawback is their reduced selectivity, especially in samples with complex matrices. The electrodes are ideal for on-site assays and rapid screening of nitrophenols and neonicotinoid pesticides in water, for the determination of single food-colorants and caffeine in different beverages and drinks

Design and characterization of colorimetric plasmonic nanostructures for imaging and sensing

Increasing demand for early disease diagnostic techniques has attracted huge interest in plasmon-based optical sensors, which can detect small concentrations of chemical and bio-analytes that are not detectable by the conventional analytic optical tools. Advances in nanofabrication techniques have driven in-depth understanding of plasmons, which result from the interactions between nano-materials and the electromagnetic fields. Precisely designing and controlling unique optical properties of plasmons have shown better sensing limits than the conventional ones by amplifying optical signals as well as detecting sensitive plasmon resonance shift upon dielectric property change on the sensing surface. In this dissertation, a series of experiments are undertaken using a colorimetric plasmonic nanocup array substrate with a single extraordinary optical transmission peak in the visible light range. Sensitive colorimetric sensing is demonstrated by detecting transmission peak shift upon the molecular adsorption or the dielectric property change on the surface. The surface modification of the plasmonic substrate using plasmonic metallic NPs is attempted in order to maximize the plasmonic sensitivity to the refractive index change through heterogeneous plasmon coupling. The plasmon coupling between the plasmons of NPs and nanostructure results in strong localized electric field and denser hot-spot formation; hence, the sensitivity is enhanced. Sensitive detections of specific bioanalytes that undergo antigen-antibody binding as well as bulk refractive index change are detected through a plasmonic dark mode shift, resulted from the heterogeneous plasmon coupling. Optical near-field interactions among plasmons, fluorophores, chromophores, and molecules are studied in order to amplify weak fluorescence, absorbance, and Raman signals from a small number of target molecules. Strong scattering field and large scattering cross-section at the plasmon resonance wavelength are the main factors for amplifying fluorescence, absorbance, and Raman scattering. Tuning plasmon resonance to target molecular optical characteristic wavelengths is critical in each application. The amplification of fluorescence is achieved by matching the plasmon resonance with the fluorescence emission band. The absorbance from chromophores, which are involved in conventional immunoassays, is enhanced by matching the chromophores’ absorbance peak with the plasmon resonance wavelength. The improved surface enhanced Raman scattering is accomplished by tuning the plasmon resonance to be close to the laser excitation wavelength. Understanding the signal amplification mechanisms from these results achieves two orders of magnitude lower limit-of-detection as well as improved sensitivity and signal-to-noise ratio. The colorimetric sensor, which is capable of enhancing fluorescence, absorbance and Raman signals from the nearby molecules, provides a versatile multifunctional sensing platform for chemical, biomedical, and environmental monitoring

Nucleic acid approaches to toxin detection

PCR is commonly used for detecting contamination of foods by toxigenic bacteria. However, it is unknown whether it is suitable for detecting toxins in samples which are unlikely to contain bacterial cells, such as purified biological weapons. Quantitative real-time PCR assays were developed for amplification of the genes encoding Clostridium botulinum neurotoxins A to F, Staphylococcal enteroxin B (SEB), ricin, and C. perfringens alpha toxin. Botulinum neurotoxins, alpha toxin, ricin and V antigen from Yersinia pestis were purified at Dstl using methods including precipitation, ion exchange, FPLC, affinity chromatography and gel filtration. Additionally, toxin samples of unknown purity were purchased from a commercial supplier. Q-PCR analysis showed that DNA was present in crudely prepared toxin samples. However, the majority of purified or commercially produced toxins were not detectable by PCR. Therefore, it is unlikely that PCR will serve as a primary toxin detection method in future. Immuno-PCR was investigated as an alternative, more direct method of toxin detection. Several iterations of the method were investigated, each using a different way of labelling the secondary antibody with DNA. It was discovered that the way in which antibodies are labelled with DNA is crucial to the success of the method, as the DNA concentration must be optimised in order to fully take advantage of signal amplification without causing excessive background noise. In general terms immuno-PCR was demonstrated to offer increased sensitivity over conventional ELISA, once fully optimised, making it particularly useful for biological weapons analysis. Finally, genetic methods for the differentiation of toxigenic Ricinus communis strains were examined, including SSR, RAPD, RFLP and SNP analysis using next generation sequencing. The results showed that the species has low genetic diversity, making genotyping a particularly difficult task, however SSR analysis was able to provide a degree of differentiation and 454 Sequencing™ identified six SNP targets that warrant further investigation in future

Nucleic acid approaches to toxin detection

PCR is commonly used for detecting contamination of foods by toxigenic bacteria. However, it is unknown whether it is suitable for detecting toxins in samples which are unlikely to contain bacterial cells, such as purified biological weapons. Quantitative real-time PCR assays were developed for amplification of the genes encoding Clostridium botulinum neurotoxins A to F, Staphylococcal enteroxin B (SEB), ricin, and C. perfringens alpha toxin. Botulinum neurotoxins, alpha toxin, ricin and V antigen from Yersinia pestis were purified at Dstl using methods including precipitation, ion exchange, FPLC, affinity chromatography and gel filtration. Additionally, toxin samples of unknown purity were purchased from a commercial supplier. Q-PCR analysis showed that DNA was present in crudely prepared toxin samples. However, the majority of purified or commercially produced toxins were not detectable by PCR. Therefore, it is unlikely that PCR will serve as a primary toxin detection method in future. Immuno-PCR was investigated as an alternative, more direct method of toxin detection. Several iterations of the method were investigated, each using a different way of labelling the secondary antibody with DNA. It was discovered that the way in which antibodies are labelled with DNA is crucial to the success of the method, as the DNA concentration must be optimised in order to fully take advantage of signal amplification without causing excessive background noise. In general terms immuno-PCR was demonstrated to offer increased sensitivity over conventional ELISA, once fully optimised, making it particularly useful for biological weapons analysis. Finally, genetic methods for the differentiation of toxigenic Ricinus communis strains were examined, including SSR, RAPD, RFLP and SNP analysis using next generation sequencing. The results showed that the species has low genetic diversity, making genotyping a particularly difficult task, however SSR analysis was able to provide a degree of differentiation and 454 Sequencing™ identified six SNP targets that warrant further investigation in future