Towards integrated multi-sensor platform using dual electrochemical and optical detection for on-site pollutant detection in water

Study on the photo/electrochemical bi-functional properties of a coupling interface of Ru[dcbpy]32+-AMT/Au by SECM imaging-based joint analytical method

A photo/electrochemical coupling interface of Ru[dcbpy]32+-AMT/Au (AMT; 5-Amino-1,3,4-thiadiazole-2-thiol) was fabricated using a dehydration condensation sulfhydrating method. For the interface functional properties, a combined dual-signal recording (CDSR) method was applied to characterize the response characteristics, and a scanning electrochemical microscopy-electrochemiluminescence (SECM-ECL) imaging was developed to assess the interface distribution uniformity. The interface biosensing compatibility was validated by constructing a simple DNA sensor. The research results show that the interaction between the two functional parameters follows a synergistic effect mechanism in the coupling conditions and an interference effect mechanism in the detection condition. Under optimized conditions, the saturation dual-signal response values are 156.0 and 86.8 μA, respectively. The statistics and imaging comparison analysis validate good interface distribution uniformity and stability performance. The DNA sensor's dual-signal detection limits to the signal probe (SP) are ∼30 fM and 0.3 pM with linear ranges of 100.0 fM ∼ 1.0 nM and 1.0 pM ∼ 10.0 nM, respectively. The fabricated interface exhibits an effective bi-functional response performance compatible with biosensing. The proposed imaging method has a high technical fit for studying photo/electrochemical coupling interfaces and can also provide a reference for other similar coupling interface analyses.

Lab-on kit: A 3D printed portable device for optical and electrochemical dual-mode detection

The hyphenation of electrochemical methods and optical methods in a single portable device is expected to be a challenging combination to enhance the information which can be gained on complex chemical systems. In this paper, a low-cost spectrophotometric device based on low-cost electronics integrated with an electroanalytical cell equipped with a screen printed electrode (SPE) and assembled exploiting a DIY approach, is presented. This easy to use device allowed spectrophotometric and electroanalytical measurements to be performed simultaneously providing simultaneous information and enabling concomitant comparison and autovalidation of the results collected. The analytical robustness and precision of the proposed system was successfully tested on solutions containing mixtures of Patent Blue (E-131) and Brilliant Blue (Erioglaucine E-133), two food dyes displaying optical and redox properties very similar to each other.

Confinement-enhanced microalgal individuals biosensing for digital atrazine assay

Microalgal sensors are widely recognized for their high sensitivity, accessibility, and low cost. However, the current dilemma of motion-induced spatial phase changes and concentration-related multiple scattering interferes with induced test instability and limited sensitivity, which has hindered their practical applications. Here, a differentiated strategy, named confinement-enhanced microalgal biosensing (C-EMB), is developed and proposed to pave the way. The in-situ printed microgel trap is designed to confine Chlamydomonas reinhardtii individuals, stabilizing their spatial phase. The microgel trap arrays are introduced to eliminate the multiple scattering of microalgae, breaking the existing effective concentration in traditional microalgal sensing and enabling sensitive assays. The integration with lab-on-a-chip technology and a developed digital imaging algorithm empower portable and automated detection. With this system, a microalgae analyzer is developed for atrazine detection, featuring a linear range of 0.04-100 μg/L. We assess the system's performance through practical atrazine assays on commercial food, using a double-blind test against a standard instrument. Our results demonstrate the good accuracy and test stability of this system with the mean bias atrazine detection in corn and sugarcane juice samples (SD) were 1.661 μg/L (3.122 μg/L) and 3.144 μg/L (4.125 μg/L), respectively. This method provides a new paradigm of microalgal sensors and should advance the further applications of microalgal sensors in commercial and practical settings.

Smart crystalline framework materials with a triazole carboxylic acid ligand: fluorescence sensing and catalytic reduction of PNP

Triazole polycarboxylic acid ligands are widely employed in the construction of MOFs due to their strong coordination ability and flexible coordination modes. In this work, three novel complexes (Pb(MCTCA)(H2O) (1), Co(HMCTCA)2(H2O)2 (2) and Cu(HMCTCA)2(H2O)2 (3)) based on the H2MCTCA ligand (5-methyl-1-(4-carboxyl)-1H-1,2,3-triazole-4-carboxylic acid) were successfully synthesized under hydrothermal conditions, respectively. X-ray single crystal structure analysis shows that complex 1 is a 3D network structure, where the central metal Pb(II) is six coordinated to form deformed triangular prism geometry. The complexes 2 and 3 are both 2D layer supramolecular structures connected through intermolecular hydrogen, where the central metals (Co/Cu) are six coordinated to form octahedral configuration geometry. Based on functional properties, it is found that complex 1 exhibits excellent detection ability for small-molecule drugs (azithromycin, colchicine and balsalazide disodium) and actinide cations (Th4+ and UO22+) within a lower concentration range without interference from other components. In particular, the detection limits of three small-molecule drugs are all lower than 0.30 μM. In addition, complexes 2 and 3 exhibited excellent catalytic reduction performance toward p-nitrophenol (PNP), with a reduction efficiency exceeding 98%. These experimental results evidence that complexes 1-3 have potential application prospects in fluorescence sensing and catalytic reduction.

A Sensitive Response Index Selection for Rapid Assessment of Heavy Metals Toxicity to the Photosynthesis of Chlorella pyrenoidosa Based on Rapid Chlorophyll Fluorescence Induction Kinetics

Heavy metals as toxic pollutants have important impacts on the photosynthesis of microalgae, thus seriously threatening the normal material circulation and energy flow of the aquatic ecosystem. In order to rapidly and sensitively detect the toxicity of heavy metals to microalgal photosynthesis, in this study, the effects of four typical toxic heavy metals, chromium (Cr(VI)), cadmium (Cd), mercury (Hg), and copper (Cu), on nine photosynthetic fluorescence parameters (φ_Po, Ψ_Eo, φ_Eo, δ_Ro, Ψ_Ro, φ_Ro, F_V/F_O, PI_ABS, and S_m) derived from the chlorophyll fluorescence rise kinetics (OJIP) curve of microalga Chlorella pyrenoidosa, were investigated based on the chlorophyll fluorescence induction kinetics technique. By analyzing the change trends of each parameter with the concentrations of the four heavy metals, we found that compared with other parameters, φ_Po (maximum photochemical quantum yield of photosystem II), F_V/F_O (photochemical parameter of photosystem II), PI_ABS (photosynthetic performance index), and S_m (normalized area of the OJIP curve) demonstrated the same monotonic change characteristics with an increase in concentration of each heavy metal, indicating that these four parameters could be used as response indexes to quantitatively detect the toxicity of heavy metals. By further comparing the response performances of φ_Po, F_V/F_O, PI_ABS, and S_m to Cr(VI), Cd, Hg, and Cu, the results indicated that whether it was analyzed from the lowest observed effect concentration (LOEC), the influence degree by equal concentration of heavy metal, the 10% effective concentration (EC₁₀), or the median effective concentration (EC₅₀), the response sensitivities of PI_ABS to each heavy metal were all significantly superior to those of φ_Ro, F_V/F_O, and S_m. Thus, PI_ABS was the most suitable response index for sensitive detection of heavy metals toxicity. Using PI_ABS as a response index to compare the toxicity of Cr(VI), Cd, Hg, and Cu to C. pyrenoidosa photosynthesis within 4 h by EC₅₀ values, the results indicated that Hg was the most toxic, while Cr(VI) toxicity was the lowest. This study provides a sensitive response index for rapidly detecting the toxicity of heavy metals to microalgae based on the chlorophyll fluorescence induction kinetics technique.

Sol-Gel Immobilized Optical Microalgal Biosensor for Monitoring Cd, Cu and Zn Bioavailability in Freshwater

While analytical measurements provide the quantitative estimation of the total amount of metals present in a sample, they do not reflect the truly bioavailable fraction of metal which reflects the adverse biological effect. Hence the development of monitoring tools for detecting bioavailable toxic metals has become a priority in environmental monitoring activities. An optical whole-cell biosensor was constructed using the microalga Scenedesmus subspicatus MM1 immobilizing in inorganic silica hydrogels using the sol-gel technique to detect bioavailable Cadmium (Cd²⁺), Copper (Cu²⁺) and Zinc (Zn⁺) in freshwater. Conditions for optimum biosensor performance have been established regarding effective pH range, cell density, exposure time, and storage stability. The optimum response for the biosensor was dependent on the pH of the matrix, cell concentration and exposure time were derived. The biosensor was operational for four weeks. The limit of detection for the algal biosensor was determined as 9.0 × 10^-1, 9.1 × 10^-1, and 8.8 × 10^-1 mg/L for Cd, Cu and Zn, respectively. Whole-cell cell biosensor will be highly useful since it comprises a single microalgal species able to detect the bioavailable content of Cd²⁺, Cu²⁺, and Zn²⁺ in freshwater.

Recent Trends in Biosensors for Environmental Quality Monitoring

The monitoring of environmental pollution requires fast, reliable, cost-effective and small devices. This need explains the recent trends in the development of biosensing devices for pollutant detection. The present review aims to summarize the newest trends regarding the use of biosensors to detect environmental contaminants. Enzyme, whole cell, antibody, aptamer, and DNA-based biosensors and biomimetic sensors are discussed. We summarize their applicability to the detection of various pollutants and mention their constructive characteristics. Several detection principles are used in biosensor design: amperometry, conductometry, luminescence, etc. They differ in terms of rapidity, sensitivity, profitability, and design. Each one is characterized by specific selectivity and detection limits depending on the sensitive element. Mimetic biosensors are slowly gaining attention from researchers and users due to their advantages compared with classical ones. Further studies are necessary for the development of robust biosensing devices that can successfully be used for the detection of pollutants from complex matrices without prior sample preparation.

Live-Cell Systems in Real-Time Biomonitoring of Water Pollution: Practical Considerations and Future Perspectives

Continuous monitoring and early warning of potential water contamination with toxic chemicals is of paramount importance for human health and sustainable food production. During the last few decades there have been noteworthy advances in technologies for the automated sensing of physicochemical parameters of water. These do not translate well into online monitoring of chemical pollutants since most of them are either incapable of real-time detection or unable to detect impacts on biological organisms. As a result, biological early warning systems have been proposed to supplement conventional water quality test strategies. Such systems can continuously evaluate physiological parameters of suitable aquatic species and alert the user to the presence of toxicants. In this regard, single cellular organisms, such as bacteria, cyanobacteria, micro-algae and vertebrate cell lines, offer promising avenues for development of water biosensors. Historically, only a handful of systems utilising single-cell organisms have been deployed as established online water biomonitoring tools. Recent advances in recombinant microorganisms, cell immobilisation techniques, live-cell microarrays and microfluidic Lab-on-a-Chip technologies open new avenues to develop miniaturised systems capable of detecting a broad range of water contaminants. In experimental settings, they have been shown as sensitive and rapid biosensors with capabilities to detect traces of contaminants. In this work, we critically review the recent advances and practical prospects of biological early warning systems based on live-cell biosensors. We demonstrate historical deployment successes, technological innovations, as well as current challenges for the broader deployment of live-cell biosensors in the monitoring of water quality.

Advances in real-time monitoring of water quality using automated analysis of animal behaviour

Monitoring of freshwater quality and its potential sudden contamination is integral to human health, sustainable economic development and prediction of pollutant impact on aquatic ecosystems. Although there have been significant advances in technologies for automated sampling and continuous analysis of water physicochemical parameters, the current capabilities for real-time warning against rapidly developing unknown mixtures of chemical hazards are still limited. Conventional chemical analysis systems are not suitable for assessing unknown mixtures of chemicals as well as additive and/or synergetic effects on biological systems. From the perspective of neurotoxicology the acute exposures to chemical agents that affect nervous system and can enter the freshwater supplies accidentally or as a result of deliberate action, can only be reliably assessed using appropriate functional biological models. In this regard real-time biological early warning systems (BEWS), that can continuously monitor behavioural and/or physiological parameters of suitable aquatic bioindicator species, have been historically proposed to fill the gap and supplement conventional water quality test strategies. Alterations in sub-lethal neuro-behavioural traits have been proven as very sensitive and physiologically relevant endpoints that can provide highly integrative water quality sensing capabilities. Although BEWS are commonly regarded as non-specific and lacking both quantitative and qualitative detection capabilities, their advantages, if properly designed and implemented, lie in continuous sensing and early-warning information about sudden alteration in water quality parameters. In this work we review the future prospects of real-time biological early warning systems as well as recent developments that are anchored in historical successes and practical deployment examples. We concentrate on technologies utilizing analysis of behavioural and physiological endpoints of animal bioindicators and highlight the existing challenges, barriers to future development and demonstrate how recent advances in inexpensive electronics and multidisciplinary bioengineering can help revitalize the BEWS field.

Small-Footprint, Field-Deployable LC/MS System for On-Site Analysis of Per- and Polyfluoroalkyl Substances in Soil

Per- and polyfluoroalkyl substances (PFASs) are emerging environmental pollutants of global concern. For rapid field site evaluation, there are very few sensitive, field-deployable analytical techniques. In this work, a portable lightweight capillary liquid chromatography (capLC) system was coupled with a small footprint portable mass spectrometer and configured for field-based applications. Further, an at-site ultrasound-assisted extraction (pUAE) methodology was developed and applied with a portable capLC/mass spectrometry (MS) system for on-site analysis of PFASs in real soil samples. The influential variables on the integration of capLC with MS and on the resolution and signal intensity of the capLC/MS setup were investigated. The important parameters affecting the efficiency of the pUAE method were also studied and optimized using the response surface methodology based on a central composite design. The mean recovery for 11 PFASs ranged between 70 and 110%, with relative standard deviations ranging from 3 to 12%. In-field method sensitivity for 12 PFASs ranged from 0.6 to 0.1 ng/g, with wide dynamic ranges (1-600 ng/g) and excellent linearities (R² > 0.991). The in-field portable system was benchmarked against a commercial lab-based LC-tandem MS (MS/MS) system for the analysis of PFASs in real soil samples, with the results showing good agreement. When deployed to a field site, 12 PFASs were detected and identified in real soil samples at concentrations ranging from 8.1 ng/g (for perfluorooctanesulfonic acid) to 2935.0 ng/g (perfluorohexanesulfonic acid).

How does the Internet of Things (IoT) help in microalgae biorefinery?

Microalgae biorefinery is a platform for the conversion of microalgal biomass into a variety of value-added products, such as biofuels, bio-based chemicals, biomaterials, and bioactive substances. Commercialization and industrialization of microalgae biorefinery heavily rely on the capability and efficiency of large-scale cultivation of microalgae. Thus, there is an urgent need for novel technologies that can be used to monitor, automatically control, and precisely predict microalgae production. In light of this, innovative applications of the Internet of things (IoT) technologies in microalgae biorefinery have attracted tremendous research efforts. IoT has potential applications in a microalgae biorefinery for the automatic control of microalgae cultivation, monitoring and manipulation of microalgal cultivation parameters, optimization of microalgae productivity, identification of toxic algae species, screening of target microalgae species, classification of microalgae species, and viability detection of microalgal cells. In this critical review, cutting-edge IoT technologies that could be adopted to microalgae biorefinery in the upstream and downstream processing are described comprehensively. The current advances of the integration of IoT with microalgae biorefinery are presented. What this review discussed includes automation, sensors, lab-on-chip, and machine learning, which are the main constituent elements and advanced technologies of IoT. Specifically, future research directions are discussed with special emphasis on the development of sensors, the application of microfluidic technology, robotized microalgae, high-throughput platforms, deep learning, and other innovative techniques. This review could contribute greatly to the novelty and relevance in the field of IoT-based microalgae biorefinery to develop smarter, safer, cleaner, greener, and economically efficient techniques for exhaustive energy recovery during the biorefinery process.

Third Generation Whole-Cell Sensing Systems: Synthetic Biology Inside, Nanomaterial Outside

Whole-cell sensing systems (WCSSs) are highly anticipated in the field of on-site detection. However, due to their low specificity, poor stability, and potential environmental problems, their commercial application is unrealistic. Recently, synthetic biology and nanomaterials have provided potential solutions to these problems, propelling WCSSs into a new generation. Synthetic biology provides a complete solution for the intelligent design and assembly of elements, modules, and genetic circuits. Nanomaterials covering the exterior of the cells provide stable protection, remote control capability, and catalytic ability for the WCSSs, and they can limit the horizontal transfer of genetic elements. These advancements enable personalized customization, intelligent control, and self-destruction in the next generation of cell sensors, promoting their industrialization.

Enhanced Stability and Amplified Signal Output of Single-Wall Carbon Nanotube-Based NH3-Sensitive Electrode after Dual Plasma Treatment

Pristine nanomaterials are normally prepared using finely controlled fabrication processes. Because no imperfect nanostructure remains, they cannot be used directly as electrode substrates of functional devices. This is because perfectly organized nanostructures or nanomaterials commonly require posttreatment to generate intentionally, the kinds of desirable defects inside or on their surfaces that enable effective functionalization. Plasma treatment is an easier, simpler and more widely used way (relative to other methods) to modify a variety of nanomaterials, although plasma-functionalized nano surfaces commonly have a short lifetime. We present herein a dual plasma treatment (DPT) that significantly enhances the degree and lifetime of plasma-induced surface functional groups on single-walled carbon nanotubes (SWCNTs). The DPT process consists of two individually optimized oxygen-plasma treatments. The DPT-modified SWCNT functioned as a sensing material for ammonia gas for more than a month. It also provided more than three times the degree of functionality for amplified signal output than with a single-plasma-treated SWCNT electrode.

An ultrasensitive biosensor for fast detection of Salmonella using 3D magnetic grid separation and urease catalysis

Screening of pathogenic bacteria plays a crucial role in preventing foodborne disease outbreaks. In this study, an ultrasensitive biosensor was developed for fast detection of Salmonella using self-assembled magnetic nanoparticle (MNP) chains for continuous-flow separation of Salmonella from large-volume sample, urease coated gold nanoparticles (GNPs) for specific labelling of Salmonella and efficient amplification of signal, and linear scan voltammetry for sensitive detection of catalysate. First, MNP chains were formed and distributed in a 3D spiral channel using mutually repelling cylindrical magnets and ring iron gears to control anti-Salmonella monoclonal antibody coated MNPs. After bacterial sample was continuous-flow drawn into the channel, bacteria-MNP complexes (magnetic bacteria) were formed on the chains, resulting in specific separation of target bacteria from sample background. Then, anti-Salmonella polyclonal antibodies and urease coated GNPs were drawn to label the magnetic bacteria, resulting in the formation of enzymatic bacteria. After washing to remove residual GNPs, urea was drawn and catalyzed by urease on enzymatic bacteria, resulting in the produce of catalysate (ammonium carbonate). Finally, the catalysate was transferred into a microfluidic chip with a thin-film Ag/AgCl reference electrode array for linear scan voltammetric measurement, and the resistance of catalysate was obtained to determine the amount of target bacteria. This biosensor could quantitatively detect Salmonella from 1.0 × 10¹ to 1.0 × 10⁶ CFU/mL in 1 h with low detection limit of 10¹ CFU/mL. The mean recovery for Salmonella in spiked milk was about 104.3%.

Micro-fabricated electrochemical chloride ion sensors: From the present to the future

The real-time detection and monitoring of chloride ion concentrations play important roles in broad industrial applications, including wearable health care device, environmental pollutant control and infrastructure corrosion monitoring. The development of all-solid-state micro-fabricated electrochemical sensors has enabled the miniaturisation of these testing devices. This study reviewed the micro-fabricated electrochemical chloride sensors developed since 1970s, together with a brief summary regarding the progression of miniaturised electrochemical sensors in the past half century. Three major types of electrochemical chloride sensors with specific ion-selectivity have been discussed, the potentiometric sensors (including both ion-selective electrodes and chemical FETs), the chronopotentiometric sensors and the voltammetric sensors. In addition, colorimetric sensors, an emerging low-cost, portable, fast diagnose sensor technique has been included in this review. Four critical sensor performances have been reviewed and compared systematically, the sensibility (chloride concentration range), selectivity, lifetime and applicable pH ranges. The future perspectives for engineering applications proposed in this review will benefit the further development of integrated multi-functional sensors, as well as new instrumental testing methods.

Development of Microalgae Biosensor Chip by Incorporating Microarray Oxygen Sensor for Pesticides Sensing

A microalgae (Pseudokirchneriella subcapitata) biosensor chip for pesticide sensing has been developed by attaching the immobilized microalgae biofilm pon the microarray dye spots (size 100 μm and pitch 200 μm). The dye spots (ruthenium complex) were printed upon SO₃-modified glass slides using a polydimethylsiloxane (PDMS) stamp and a microcontact printer (μCP). Emitted fluorescence intensity (FI) variance due to photosynthetic activity (O₂ production) of microalgae was monitored by an inverted fluorescent microscope and inhibition of the oxygen generation rate was calculated based on the FI responses both before and after injection of pesticide sample. The calibration curves, as the inhibition of oxygen generation rate (%) due to photosynthetic activity inhibition by the pesticides, depicted that among the 6 tested pesticides, the biosensor showed good sensitivity for 4 pesticides (diuron, simetryn, simazine, and atrazine) but was insensitive for mefenacet and pendimethalin. The detection limits were 1 ppb for diuron and 10 ppb for simetryn, simazine, and atrazine. The simple and low-cost nature of sensing of the developed biosensor sensor chip has apparently created opportunities for regular water quality monitoring, where pesticides are an important concern.

Biotechnological Advances in the Design of Algae-Based Biosensors

In addition to their use in biomass production and bioremediation, algae have been extensively exploited in biosensing applications. Algae-based biosensors have demonstrated potential for sensitive, sustainable, and multiplexed detection of analytes of agroenvironmental and security interest. Their advantages include the availability of different algal bioreceptors including whole cells and their photosynthetic subcomponents, their potential to be integrated into dual transduction miniaturized devices, and the opportunity for continuous environmental monitoring. Despite obstacles including limited stability and selectivity, algae-based biosensing is a realistic prospect that has some recent effective applications. Strategic exploitation of cutting-edge technologies including materials science, nanotechnology, microfluidics, and genome editing will help to achieve the full potential of algae-based sensors.