Abstract
Pathogenic illnesses that are transmitted through food and water sources are admitted as a global problem with significant morbidity and mortality rates. Therefore, the monitoring of food- and water-borne pathogens is a critical aspect of control. The large number of investigations has recently been emphasized analytical techniques to build a strategy for fast, sensitive, and accurate monitoring of food- and water-borne pathogens employing nanomaterials. Irrespective of several efforts in ensuring the food- and water safety, food- and water-borne outbreaks are evident around the world. In pathogen detection and monitoring, electrochemical biosensors based on nanomaterials have gotten a lot of interest. Various types of nanomaterials and electrochemical technological solutions have improved the innovative diagnostics tools to detect the food- and water-borne pathogens. Nanomaterial that includes quantum dots, gold, silver, magnetic, metal oxides, and carbon-based nanomaterials that can be functionalized with biomarkers are commonly used for pathogen detections. Recently, the nanocomposites combined with these functionalized nanomaterials have enhanced the more sensitive, rapid, accurate, and cost-effective biosensors. The proper assessments of pathogens on food and water, along with their quality monitoring, are critical variables in making policy decisions about the infrastructure of food and water distribution networks, the efficient water treatment, and the prevention of food- and water-borne epidemics.
1. Introduction
Several water-based poisons can be lethal to animals if they breath them. Water- and food-borne infections, such as diarrhea, gastrointestinal ailments, and systemic illnesses, are a global issue which are estimated to kill millions of people every year [1, 2]. Children account for almost 1.4 million of these deaths [1]. Diarrheal diseases are the most frequent due to malnutrition in newborns and kids. However, many pathogenic organisms have known to cause food- and water-borne illnesses that include Campylobacter, Clostridium perfringens, Escherichia coli O157:H7, Helicobacter pylori, Listeria monocytogenes, Norovirus, Salmonella, Shigella spp., Staphylococcus aureus, Toxoplasma gondii, and Vibrio cholera. These bacterial food- and water-borne pathogens have been reported for major cause of death worldwide [1, 2].
To minimize the occurrence of food-borne disease, identification and monitoring of food- or water-borne microorganisms are essential. Traditional methods of detection of for these pathogens rely on growing them on the agar plates which are exhausting processes and take more than three days to a week, from preliminary observations to confirmation of the pathogens, respectively [3]. However, cultural methods of detection are insufficient, and many pathogens are unculturable. Demands are kept on increasing for more quick process for the detection of food- and water-borne pathogen for prevention of infectious diseases, to assure food safety and to preserve public health.
Water-borne infectious agents are a major cause of diarrhea-related morbidities and mortalities around the world. Many zoonotic illnesses are spread whenever animal/human excreta are not adequately obtained, accumulated, or treated before disposal of wastes to environments like nearby local water bodies. Agriculture-based wastes and storm runoff can spread these organisms across many medium including soils, waters, and aerosols that allow them to settle in places where humans or animals could be exposed and afflicted. Water-borne infectious agents when exposed, breath, touch or consumed by humans or animals, it could cause serious sickness [4]. Illness reported from water-borne toxins and toxigenic microbes are known to spread by direct contacts or consumption of contaminated water as well as aquatic species. Poisoning symptoms are also reported in humans after eating seafood and shellfish that contains water-borne toxins. Toxic substances can build up in salt water, fresh water, and brackish water bodies that result in harmful algal blooms. However, they are known to bioaccumulate in the food webs of the aquatic system, infects the fishes, shore birds, marine mammals, and other species. Exposure via inhalation through respiratory tract depends on the toxin or toxin-producing infectious agents. Inhaling aerosolized harmful algal particles can cause respiratory discomfort and asthma episodes in humans.
2. Food- and Water-Borne Pathogens: Global Scenario
A range of infectious organisms, including bacteria, viruses, protozoa, and helminths, cause waterborne diseases through ingestion, aerosol contact, or contact with contaminated water [5, 6]. Around 780 million people in the globe are inaccessible to clean water, and an estimate of 2.5 billion people are inaccessible to proper sanitizing faculties [7]. The global incidence of food-borne diseases is efficient to measure. According to CDC 2011, an estimate of 1 in 6 Americans (48 million) will become ill, around 128,000 estimates to be hospitalized, and 3,000 death each year from food-borne infections [8, 9].
The pollution of food and drinking water are commonly involved in the outbreak of disease. Early detection of food- and water-borne diseases reduces the number of death and infections. Fast and precise detection methods are necessary for convenient handling. In comparison to other traditional and molecular approaches, nanosensors have higher efficacy. Early detection reduces health risk and improves the overall quality of life.
3. Current Methods of Detection of Food- and Water-Borne Pathogens and Their Limitations
There is currently no consistent approach for collecting and analyzing all pathogenic microorganisms of relevance from food and water samples [10]. For the inhibitors present in the samples of polluted water or food, the most common protocols for sampling, culture-dependent, and zoonotic pathogen detection are posing challenges in the detection methods. The established general protocols for sample collection, culture-independent detection method, and detection of zoonotic pathogens are some of the challenges of the detection methods.
Higher specificities, sensitivities, reproducibility, rapid, automation, and cost-effective are the most significant prerequisites for reliable analysis [11]. The culture-dependent methods are widely applying to identify large number of pathogens in food- and water borne diseases. However, due to other bacterial interference, it affects this methods sensitive and need long time to obtain the results. Further, due to large number of pathogens that is unculturable and culture-based methods produces false negative results as well [3, 12].
Index of pathogens for water quality monitoring has been chosen for both culture and molecular approaches to show the higher percentages of pathogens in the water. Among them, E. coli has been widely used because pathogen detection methods are relatively simple and inexpensive. However, the major disadvantage of detecting E. coli will not provide information on the pathogen’s host origin, and, in some cases, they are not associated with the pathogens in food- and water-like virus and protozoans [13].
Molecular approaches are highly specific to detect the certain species of pathogens and provide additional pathogen phylogenetic information [14]. Alternative indicators that are easily related to the host source can be used with these strategies. This allows for the differentiation of human and animal diseases as well as the tracing of pollution sources [13, 15]. It has been argued that host-origin libraries based on phenotypic approaches could be beneficial for identifying pathogen sources but developing such libraries could be expensive [16]. As a result, molecular approaches appear to be better adapted for assessing health risks.
There are a variety of molecular approaches available now for detecting various infections. They are used to assess food and water microbiological quality, pathogen removal efficiency in drinking and wastewater treatment plants, food, and microbial source-tracking (MST) techniques [17]. Tables 1 and 2 show some examples of detection methods for food- and water-borne pathogens, as well as their detection limits. Molecular-based approaches that include nucleic acid amplification techniques can provide sensitive and analytical instruments for detection of various types of pathogens including emerging variants. These methods also provide scope for automation and real time analysis of microbial risk assessment [17].
4. Applications of Nanomaterials (NMs) in Monitoring Food- and Water-Borne Pathogens
Nano-based sensors are used in measuring of biological response that converts the response signals for interpretation and analysis. However, the selection of NMs for such sensing applications depends on the properties of the NMs (Table 3).
NMs-based sensors have reported to for higher sensitivity and specific in nature in comparison to that of material-based sensors. Common NMs used in sensor technology are shown in Figure 1.
To maximize the specificity of the biological reaction, the nanosensors can be controlled at a scale equivalent to biological mechanisms. “Nanofabrication” is a key stage in design of experiments before adding the NMs for the application of sensing. Majorly, it includes two crucial steps: The first step needs the fabrication and design of nano-adhesive using integrated circuits, and the second involves the engineering of NMs surface using micro-machining procedures. Chemical bonding, photolithography, surface etching techniques, and thin film etching or growth are four key processes involved in biosensing through nanofabrication.
In the increase of chronic diseases such as diabetes and cancer, there is a need for a broad awareness of early-stage disease detection using biosensors, which provide a quick reaction and high sensitivity in the early stages. The lithography technique is a commonly used fundamental process in nanofabrication and is used to create nanoscale electrodes. NMs give a larger surface area-to-volume for immobilization of biological agents that can be more sensitivity and specific in biosensing [47].
The usage of enzyme glucose oxidase was used to construct glucose biosensors, and the detection of glucose was increased by the use of Pt NPs on the carbon nanotubes (CNTs). Such biosensors can detect glucose from a variety of sources other than blood. These applications are also useful for immunosensors that are based on antigen-antibody complexes for quick and better detection of antigens [48].
5. Nanomaterial-Based Sensors to Detection of Food- and Water-Borne Pathogens
Many present water quality sensors can be replaced with nanotechnology enabled sensors. Others have stated that the nanosensor can monitor an analyte which should be fast with reversible binding. However, the nano-probe can be selective to detect specific microorganisms/chemical with higher sensitive which do not need for reversibility [49]. For the sake of clarity, the word “nanosensor” refers to any sensor platform that makes use of NMs distinctive optical, electrical, or magnetic capabilities to improve the detection of analyte. A variety of nanosensors are reported for more sensitive detection of pH, infections, and toxins in water that have been proposed [49–52]. Basically, nanosensors consist of three parts, namely, a suitable NM, recognition element, and mechanism for signal processing [53].
The recognition element interacts with the analytes of interest, resulting in a detectable signal that is recorded [52]. The specificity of nanosensor can be obtained by sensing an intrinsic signal obtained either from the analyte or from the recognition elements upon binding. The sensitivity of the nanosensor can be determined optical, electrical, or magnetic properties of the material and their signal processing technologies upon detection of signals upon analyte interaction.
Many nanosensors have extremely low detection limits reported in the literature; however, these detection limits are rarely confirmed under real-world circumstances that represent water quality on the ground. Additionally, due to the significantly small scale of a nanosensor-based detection system, it ensures the efficient detection of biological elements such antigen-antibody, bacteria, and viruses. Sample pretreatment such as purification and concentration may be required for better detection after the deployment of nanosensors.
Microfluidic separation [54, 55] and NMs-based isolation [56] are two fast-evolving technologies for pretreatment, as are more standardized filtering [57] and centrifugation-based methodologies. Many sensor research facilities focus on sample pretreatment, which is not covered in depth here. The types of NMs in nanosensors, the analytes they detect, and the signal transduction method used to monitor analyte recognition can all be classed. For the sake of simplicity, it can be address only nanosensors that use the most widely is signal transduction methods: optical, electrical, and magnetic. The range of NMs used in water-quality nanosensors is summarized in Table 4. There are detailed explanations of the many types of NMs used in nanosensors elsewhere [50, 58–61].
5.1. Optical Signal Transduction
When the target analyte interacts with NMs in an optical sensor, a signal is produced. This method is widely used due to its overall ease of use, a quick reading, and practical sensitivity. The most common optical signal transduction techniques are fluorescence and surface plasmon-enabled spectroscopies.
Fluorescence is defined as the measurement of a fluorophore’s emission when it returns to its ground state after being excited by light. Quantum dots, metal-based NMs, and up-conversion NMs are among the fluorescent NMs being studied for their sensing uses. Ng et al. [61] have highlighted many of the exciting discoveries in the utilization of fluorescent NMs for sensing applications.
When noble metal-based NMs, such as gold and silver, are activated by light, surface plasmons (e.g., coherently oscillating surface electrons) can form, generating strong electromagnetic fields near the NM surface (within a few nanometers) [62]. The size, shape, identity, and local environment that surrounds the NM all influence the frequency at which the surface electrons resonant, resulting in an absorption band known as the localized surface plasmon resonance (LSPR). The surface-enhanced Raman spectroscopy (SERS) and colorimetric (absorption) approaches are two types of signal transduction that use LSPR.
In the region of the noble metal surface, LSPR generates a stronger electromagnetic field. The Raman cross-sections of target analytes are raised by several magnitudes when they are in this enhanced electromagnetic environment. This augmentation is known as SERS. A SERS spectrum reflects the analyte’s distinctive covalent bonds, while the SERS is a vibrational spectroscopic technique. If the signal from this “fingerprint” spectrum is strong enough, it can be used to determine whether an analyte is present in a complex matrix. SERS has demonstrated the ability to identify single molecules in this intrinsic detection mode [63], but often for non-environmentally significant analytes beneath demanding instrumental working circumstances. The implementation of SERS for water-contaminant quantification is hindered by the requirement that the “hot spots” largely responsible for SERS enhancement be less than 5 nm in size, excluding big analytes [60]. This characteristic, combined with the requirement that the analyte binds to the noble metal nanoparticle surface, may make SERS ineffective for intrinsic analyte detection. The alternative, and more extensively used, technique is to use affinity ligands like antibodies and aptamers to enhance the properties of the nanoparticle surface [64]. Because of the method’s high sensitivity and multiplex capacity, very sensitive, hand-held Raman spectrometers are becoming more affordable; it is expected that SERS will gradually come to occupy a larger piece of the nanosensor armamentarium [65].
Colorimetric sensing is a simpler kind of LSPR that includes monitoring the aggregation status of NPs. Color variations (usually red to blue for spherical gold NPs; yellow to brown for spherical silver NPs) represent the coupling of surface plasmons on nearby particles when NPs become destabilized. These color changes can be observed visually or with the aid of a spectrophotometer. There have been a lot of aggregation-based tests for water-borne chemicals and microorganisms (Table 4) [59]. Incorporating such assays into minimal paper-based colorimetric assays can make them field-deployable [55].
5.2. Electrical Signal Transduction
The high conductivity and excellent stability of silicon, noble metal–based NMs (Pt, Ag, and Au), carbon-containing nanomaterials (graphene and CNTs), and inorganic two-dimensional nanosheets are used in electrical signal transduction. Chemiresistors, field-effect transistors, and electrochemical sensors are the three types of electrically based nanosensors [50]. Chemiresistors are electrical circuits that change resistance when an analyte interacts with the sensor surface. The mobility of a charge carrier (i.e., analyte) travelling through channels subjected to an applied electric field controlled by a conductive gate electrode is measured using field-effect transistors (FETs). A change in signal is noticed when an analyte enters the channel. In Cui and Lieber’s pioneering work in 2001 [66], the FET-based nanosensor platforms were in development. Electrochemical sensors detect voltage or current changes that occur when the electrons transfer from the sensor surface to a target analyte or intermediate. The addition of recognition elements (antibodies, aptamers) to chemiresistors, FETs, or electrochemical sensors has enabled sensitive detection of aquatic pollutants such as E. coli [67] and hepatitis C [68].
5.3. Magnetic Signal Transduction
The signal is generated with the NM in optical sensors interact with the target analyte. The signal is processed, and this method is commonly used because it is easy to use, rapid, and practically sensitive. The optical transduction signal may be fluorescence-based and SPR-enabled technology.
The magnetic NMs can respond to an external magnetic field and their functionalization with analyte specific proteins allows for magnetic isolation of analytes, which can subsequently be detected [69]. The size and chemical identity of NMs determine particle magnetism, which is determined by their final application. Magnetic particles are made from several materials, including metallic iron, iron oxides, cobalt, nickel, and a variety of multi-element compounds. Due to their presumed biocompatibility and lower-cost manufacturing, iron-based NMs (e.g., FeO, Fe3O4, and -Fe2O3) are of special interest.
Magnetoresistance, hydrodynamic properties, and T2 relaxation nuclear magnetic resonance are three types of magnetic signal detecting methodologies. Magnetoresistance sensors change an electrical resistance when magnetic nanoparticle-labelled analytes bind to them, and they have recently been employed to detect Mycobacterium bovis [70] and influenza A [71]. Monitoring nanoparticle relaxation exercises dynamics in a time-dependent magnetic field can reveal changes in hydrodynamic characteristics caused by analyte-induced nanoparticle clustering. This method has been utilized to detect Bacillus globigII spores in a field-deployable application [72]. The magnetic NPs start to aggregate in presence of an analyte which can be used in magnetic resonance imaging through monitoring of the change in the T2 (e.g., spin-spin) water proton relaxation time. Using this method, it is successful in the detection of Salmonella enterica and Newcastle disease virus [73].
6. Conclusion and Future Perspective
Food-borne and water-borne infectious organisms possess a threat for public health hazards, cause of serious illness and death. Therefore, an effective microbiological surveillance, detection of infectious agents and assessment of health risks is required to achieve the safe and disease-free food products and water for drinking.
Traditional methods for detecting food-borne and water-borne pathogens, which rely on growing microorganisms, are selective and specific but time-consuming and laborious. A variety of quick detection methods must be created to address the shortcomings of traditional detection systems. Traditional methods are low sensitive, nonspecific, time-efficient, and dependent methods rather than rapid detection systems. Molecular-based technologies that use the DNA and RNA used the PCR, RTPCR, mPCR, and DNA microarray which are more sensitive and specific but need the skilled labor and high-cost instruments.
Nanotechnology has been hailed as a game changer in a variety of fields. Despite their increasing popularity, nanotechnologies for detection of pathogens in food and water are still in development, with most pathogen nanosensors or assays still in the proof-of-concept stage. The degree of improvement brought about by nanotechnology, on the other hand, varies. Because of a bulkier architecture and fewer access and reaction centers, certain strategies increase dramatically, while others improve only somewhat. This is notably true for whole-cell detection.
The utilization of nanosensors in food sector that benefits the food safety aspects seems to be a rapid, real time, easy, and cost-effective method to detect the contaminations by pathogens and their toxins. Further, these types of nanosensors can be automated for high throughput and portable for the screening the infectious agents and toxic materials from the variety of food and water samples.
Furthermore, a variety of biosensor-based approaches have the potential to address the demand for downsizing as well as low-cost analytical instruments. Biosensor-based approaches are simple to use and do not necessitate the use of trained staff.
It is also feasible to employ a combination of many fast methods to detect a specific food-borne disease, as using only one method may not be enough to confirm the discovered infection. To establish the most effective and accurate detection approach for food-borne pathogens, more research into the effects of diverse combinations of fast methods is needed.
Researchers will be able to construct highly sensitive, selective, and unobtrusive nanosensors for evaluating food-borne microorganisms at an affordable cost thanks to considerable research advancements in nanotechnology for nanomaterial exploration and the development of novel processes in the future. Biosensor-based approaches are simple to use and do not necessitate the use of trained staff.
Abbreviations
| ELISA: | Enzyme-linked immunosorbent assay |
| SERS: | Surface-enhanced Raman spectroscopy |
| FISH: | Fluorescent in situ hybridization |
| LFA: | Laser flash analyzer |
| SPR: | Surface plasmon resonance |
| LSPR: | Localized surface plasmon resonance |
| IMS: | Integrated medical systems |
| PCR: | Polymerase chain reaction |
| NMR: | Nuclear magnetic resonance |
| SALDI-MS: | Surface-assisted laser desorption/ionized mass spectroscopy |
| VBNC: | Viable but non-culturable |
| MST: | Microbial source tracking |
| rGO: | Reduced graphene oxide |
| OP: | Organophosphorus pesticides |
| GCE: | Glassy carbon electrode |
| ATCL: | Acetylthiocholine chloride |
| SDBS: | Sodium dodecylbenzene sulphonate |
| MFnS: | Magneto-fluorescent nanosensors |
| CFU: | Colony-forming unit |
| FET’s: | Field-effect transistors |
| VOC’s: | Volatile organic compounds |
| SiNWs: | Silicon nanowires |
| LAMP: | Loop-mediated isothermal amplification |
| NASBA: | Nucleic acid sequence-based amplification |
| NGS: | Next generation sequencing |
Conflicts of Interest
There is no conflict of interest.
Acknowledgments
The research was supported by the Strategic Academic Leadership Program of the Southern Federal University (“Priority 2030”).