Amplification of electrochemical signal by a whole-cell redox reactivation module for ultrasensitive detection of pyocyanin

Selective bioelectronic sensing of pharmacologically relevant quinones using extracellular electron transfer in Lactiplantibacillus plantarum

Redox-active small molecules containing quinone functional groups play important roles as pharmaceuticals, but can be toxic if overdosed. Despite the need for a fast and quantitative method to detect quinone and its derivatives, current sensing strategies are often slow and struggle to differentiate between structural analogs. Leveraging the discovery that microorganisms use certain quinones to perform extracellular electron transfer (EET), we investigated the use of Lactiplantibacillus plantarum as a whole-cell bioelectronic sensor to selectively sense quinone analogs. By tailoring the native EET pathway in L. plantarum, we enabled quantitative quinone sensing of 1,4-dihydroxy-2-naphthoic acid (DHNA) - a gut bifidogenic growth stimulator. We found that L. plantarum could respond to environmental DHNA within seconds, producing concentration-dependent electrical signals. This sensing capacity was robust in different assay media and allowed for continuous monitoring of DHNA concentrations. In a simulated gut environment containing a mixed pool of quinone derivatives, this tailored EET pathway can selectively sense pharmacologically relevant quinone analogs, such as DHNA and menadione, amongst other structurally similar quinone derivatives. We also developed a multivariate model to describe the mechanism behind this selectivity and found a predictable correlation between quinone physiochemical properties and the corresponding electrical signals. Our work presents a new concept to selectively sense quinone using whole-cell bioelectronic sensors and opens the possibility of using probiotic L. plantarum for bioelectronic applications in human health.

Recent Developments and Applications of Microbial Electrochemical Biosensors

This chapter provides a comprehensive overview of microbial electrochemical biosensors, which are a unique class of biosensors that utilize the metabolic activity of microorganisms to convert chemical signals into electrical signals. The principles and mechanisms of these biosensors are discussed, including the different types of microorganisms that can be used. The various applications of microbial electrochemical biosensors in fields such as environmental monitoring, medical diagnostics, and food safety are also explored. The chapter concludes with a discussion of future research directions and potential advancements in the field of microbial electrochemical biosensors.

Mechanism and applications of bidirectional extracellular electron transfer of Shewanella

Electrochemically active microorganisms (EAMs) play an important role in the fields of environment and energy. Shewanella is the most common EAM. Research into Shewanella contributes to a deeper comprehension of EAMs and expands practical applications. In this review, the outward and inward extracellular electron transfer (EET) mechanisms of Shewanella are summarized and the roles of riboflavin in outward and inward EET are compared. Then, four methods for the enhancement of EET performance are discussed, focusing on riboflavin, intracellular reducing force, biofilm formation and substrate spectrum, respectively. Finally, the applications of Shewanella in the environment are classified, and the restrictions are discussed. Potential solutions and promising prospects for Shewanella are also provided.

An extracellular electron transfer enhanced electrochemiluminescence aptasensor for Escherichia coli analysis

As a crucial indicator in food and water safety testing, the detection of Escherichia coli plays a significant role in maintaining environmental sanitation and promoting public health. Herein, based on the electrochemical activity characteristics of E. coli, we established an enhanced electrochemiluminescence aptasensor for E. coli analysis. This study presents a new method for accurate identification by utilizing a double aptamer recognition system. Specifically, a nano-cadmium sulfide (CdS) modified aptamer was used for primary labeling, while a second aptamer was immobilized on a graphene/chitosan composite electrode for re-capture. The use of two aptamers improves the accuracy of the identification process. Furthermore, the application of an electrode potential facilitates continuous electron transfer between the electrode and electrochemically active microorganisms, resulting in an enhanced electroluminescence signal in relation to the metabolic status. This strategy possesses better sensitivity, accuracy, and stability, demonstrating its potential for E. coli analysis.

Smart Design of Sensor-Coated Surgical Sutures for Bacterial Infection Monitoring

Virtually, all implantable medical devices are susceptible to infection. As the main healthcare issue concerning implantable devices is the elevated risk of infection, different strategies based on the coating or functionalization of biomedical devices with antiseptic agents or antibiotics are proposed. In this work, an alternative approach is presented, which consists of the functionalization of implantable medical devices with sensors capable of detecting infection at very early stages through continuous monitoring of the bacteria metabolism. This approach, which is implemented in surgical sutures as a representative case of implantable devices susceptible to bacteria colonization, is expected to minimize the risk of worsening the patient's clinical condition. More specifically, non-absorbable polypropylene/polyethylene (PP/PE) surgical sutures are functionalized with conducting polymers using a combination of low-pressure oxygen plasma, chemical oxidative polymerization, and anodic polymerization, to detect metabolites coming from bacteria respiration. Functionalized suture yarns are used for real-time monitoring of bacteria growth, demonstrating the potential of this strategy to fight against infections.

Tailoring the whole-cell sensing spectrum with cyborgian redox machinery

Whole-cell biosensors are an important class of analytical tools that offer the advantages of low cost, facile operation, and unique reproduction/regeneration ability. However, it has always been quite challenging to expand the sensing spectrum of the host. Here, a new approach to extend the cell sensing spectrum with biomineralized nanoparticles is developed. The nano-biohybrid design comprise biomineralized FeS nanoparticles firmly anchored onto the bacterium, Shewanella oneidensis MR-1, wherein the nanoparticles are wired to the cellular electron transfer machinery (MtrCAB/OmcA) of the bacterium, forming an artificial cyborgian redox machinery consisting of FeS-MtrCAB/OmcA-FccA. Strikingly, with this cyborgian redox machinery, the sensing spectrum of FeS hybridized S. oneidensis MR-1 cell is successfully expanded to enable whole-cell electrochemical detection of Vitamin B12, while an unhybridized native cell is incapable of sensing. This proof-of-concept nano-biohybrid design offers a new perspective on manipulating the microbial toolkit for an expanded sensing spectrum in whole-cell biosensors.

A review of highly sensitive electrochemical genosensors for microRNA detection: A novel diagnostic platform for neurodegenerative diseases diagnostics

The significant role of microRNAs in regulating gene expression and in disease tracking has handed the possibility of robust and accurate diagnosis of various diseases. Measurement of these biomarkers has also had a significant impact on the preparation of natural samples. Discovery of miRNAs is a major challenge due to their small size in the real sample and their short length, which is generally measured by complex and expensive methods. Electrochemical nanobiosensors have made significant progress in this field. Due to the delicate nature of nerve tissue repair and the significance of rapid-fire feature of neurodegenerative conditions, these biosensors can be reliably promising. This review presents advances in the field of neurodegenerative diseases diagnostics. At the same time, there are still numerous openings in this field that are a bright prospect for researchers in the rapid-fire opinion of neurological diseases and indeed nerve tissue repair.

Bio-Nanohybrid Cell Based Signal Amplification System for Electrochemical Sensing

A signal amplification system for electrochemical sensing was established by bio-nanohybrid cells (BNC) based on bacterial self-assembly and biomineralization. The BNC was constructed by partially encapsulating a Shewanella oneidensis MR-1 cell with the self-biomineralized iron sulfide nanoparticles. The iron sulfide nanoparticle encapsulated BNCs showed high transmembrane electron transfer efficiency and was explored as a superior redox cycling module. Impressively, by integrating this BNC redox cycling module into the electrochemical sensing system, the output signal was amplified over 260 times compared to that without the BNC module. Uniquely, with this BNC redox cycling system, ultrasensitive detection of riboflavin with an extremely low LOD of 0.2 nM was achieved. This work demonstrated the power of BNC in the area of biosensing and provided a new possibility for the design of a whole cell redox cycling based signal amplification system.

Yeast-induced formation of graphene hydrogels anode for efficient xylose-fueled microbial fuel cells

Microbial fuel cells (MFCs) are of great interest due to their capability to directly convert organic compounds to electric energy. In particular, MFCs technology showed great potential to directly harness the energy from xylose in the form of bioelectricity and biohydrogen simultaneously. Herein, we report a yeast strain of Cystobasidium slooffiae JSUX1 enabled the reduction and assembly of graphene oxide (GO) nanosheets into three-dimensional reduced GO (3D rGO) hydrogels on the surface of carbon felt (CF) anode. The autonomously self-modified 3D rGO hydrogel anode entitled the yeast-based MFCs with two times enhancement on bioelectricity and biohydrogen production from xylose. Further analysis demonstrated that the 3D rGO hydrogel attracted more yeast cells and reduced the interfacial charge transfer resistance, which was the underlying mechanism for the improvement of MFCs performance. This work offers a new strategy to reinforce the performance of yeast-based MFCs and provides a new opportunity to efficiently harvest energy from xylose.

Recent advances in flexible and wearable sensors for monitoring chemical molecules

In recent years, real-time health management has received increasing attention, benefiting from the rapid development of flexible and wearable devices. Conventionally, flexible and wearable devices are used for collecting health data such as electrophysiological signals, blood pressure, heart rate, etc. The monitoring of chemical factors has shown growing significance, providing the basis for the screening, diagnosis, and treatment of many diseases. Nowadays, in order to understand the health status of the human body more comprehensively and accurately, researchers in the community have started putting effort into developing wearable devices for monitoring chemical factors. Progressively, more flexible chemical sensors with wearable real-time health-monitoring functionality have been developed thanks to advances relating to wireless communications and flexible electronics. In this review, we describe the variety of chemical molecules and information that can currently be monitored, including pH levels, glucose, lactate, uric acid, ion levels, cytokines, nutrients, and other biomarkers. This review analyzes the pros and cons of the most advanced wearable chemical sensors in terms of wearability. At the end of this review, we discuss the current challenges and development trends relating to flexible and wearable chemical sensors from the aspects of materials, electrode designs, and soft-hard interface connections.

Advanced detection and sensing strategies of Pseudomonas aeruginosa and quorum sensing biomarkers: A review

Pseudomonas aeruginosa (P. aeruginosa), a ubiquitous opportunistic pathogen, can frequently cause chronic obstructive pulmonary disease, cystic fibrosis and chronic wounds, and potentially lead to severe morbidity and mortality. Timely and adequate treatment of nosocomial infection in clinic depends on rapid detection and accurate identification of P. aeruginosa and its early-stage antibiotic susceptibility test. Traditional methods like plating culture, polymerase chain reaction, and enzyme-linked immune sorbent assays are time-consuming and require expensive equipment, limiting the rapid diagnostic application. Advanced sensing strategy capable of fast, sensitive and simple detection with low cost has therefore become highly desired in point of care testing (POCT) of nosocomial pathogens. Within this review, advanced detection and sensing strategies for P. aeruginosa cells along with associated quorum sensing (QS) molecules over the last ten years are discussed and summarized. Firstly, the principles of four commonly used sensing strategies including localized surface plasmon resonance (LSPR), surface-enhanced Raman spectroscopy (SERS), electrochemistry, and fluorescence are briefly overviewed. Then, the advancement of the above sensing techniques for P. aeruginosa cells and its QS biomarkers detection are introduced, respectively. In addition, the integration with novel compatible platforms towards clinical application is highlighted in each section. Finally, the current achievements are summarized along with proposed challenges and prospects.

Recent advances in electrochemical strategies for bacteria detection

Introduction: Bacterial infections have always been a major threat to public health and humans' life, and fast detection of bacteria in various samples is significant to provide early and effective treatments. Cell-culture protocols, as well-established methods, involve labor-intensive and complicated preparation steps. For overcoming this drawback, electrochemical methods may provide promising alternative tools for fast and reliable detection of bacterial infections. Methods: Therefore, this review study was done to present an overview of different electrochemical strategy based on recognition elements for detection of bacteria in the studies published during 2015-2020. For this purpose, many references in the field were reviewed, and the review covered several issues, including (a) enzymes, (b) receptors, (c) antimicrobial peptides, (d) lectins, (e) redox-active metabolites, (f) aptamer, (g) bacteriophage, (h) antibody, and (i) molecularly imprinted polymers. Results: Different analytical methods have developed are used to bacteria detection. However, most of these methods are highly time, and cost consuming, requiring trained personnel to perform the analysis. Among of these methods, electrochemical based methods are well accepted powerful tools for the detection of various analytes due to the inherent properties. Electrochemical sensors with different recognition elements can be used to design diagnostic system for bacterial infections. Recent studies have shown that electrochemical assay can provide promising reliable method for detection of bacteria. Conclusion: In general, the field of bacterial detection by electrochemical sensors is continuously growing. It is believed that this field will focus on portable devices for detection of bacteria based on electrochemical methods. Development of these devices requires close collaboration of various disciplines, such as biology, electrochemistry, and biomaterial engineering.

Detection of Pseudomonas aeruginosa quorum sensing molecules at an electrified liquid|liquid micro-interface through facilitated proton transfer

Miniaturization of electrochemical detection methods for point-of-care-devices is ideal for their integration and use within healthcare environments. Simultaneously, the prolific pathogenic bacteria Pseudomonas aeruginosa poses a serious health risk to patients with compromised immune systems. Recognizing these two factors, a proof-of-concept electrochemical method employing a micro-interface between water and oil (w/o) held at the tip of a pulled borosilicate glass capillary is presented. This method targets small molecules produced by P. aeruginosa colonies as signalling factors that control colony growth in a pseudo-multicellular process known as quorum sensing (QS). The QS molecules of interest are 4-hydroxy-2-heptylquinoline (HHQ) and 2-heptyl-3,4-dihydroxyquinoline (PQS, Pseudomonas quinolone signal). Hydrophobic HHQ and PQS molecules, dissolved in the oil phase, were observed electrochemically to facilitate proton transfer across the w/o interface. This interfacial complexation can be exploited as a facile electrochemical detection method for P. aeruginosa and is advantageous as it does not depend on the redox activity of HHQ/PQS. Interestingly, the limit-of-linearity is reached as [H+] ≈ [ligand]. Density functional theory calculations were performed to determine the proton affinities and gas-phase basicities of HHQ/PQS, as well as elucidate the likely site of stepwise protonation within each molecule.

Electrochemical detection of redox molecules secreted by Pseudomonas aeruginosa - Part 1: Electrochemical signatures of different strains

During infections, fast identification of the microorganisms is critical to improve patient treatment and to better manage antibiotics use. Electrochemistry exhibits several advantages for rapid diagnostic: it enables easy, cheap and in situ analysis of redox molecules in most liquids. In this work, several culture supernatants of different Pseudomonas aeruginosa strains (including PAO1 and its isogenic mutants PAO1ΔpqsA, PA14, PAK and CHA) were analyzed by square wave voltammetry on glassy carbon electrode during the bacterial growth. The obtained voltamograms shown complex traces exhibiting numerous redox peaks with potential repartitions and current amplitudes depending on the studied bacterium and/or growth time. Among them, some peaks were clearly associated to the well-known redox toxin Pyocyanin (PYO) and the autoinducer Pseudomonas Quinolone Signal (PQS). Other peaks were observed that are not yet attributed to known secreted species. Each complex electrochemical response (number of peaks, peak potential and amplitude) can be interpreted as a fingerprint or "ID-card" of the studied strain that may be implemented for fast bacteria strain identification.

DNA-Origami-Based Assembly of Au@Ag Nanostar Dimer Nanoantennas for Label-Free Sensing of Pyocyanin

Early-stage detection of diseases caused by pathogens is a prerequisite for expedient patient care. Due to the limited signal-to-noise ratio, molecular diagnostics needs molecular signal amplification after recognition of the target molecule. In this present study, we demonstrate the design of plasmonically coupled bimetallic Ag coated Au nanostar dimers with controlled nanogap using rectangular DNA origami. We further report the utility of the designed nanostar dimer structures as efficient SERS substrate for the ultrasensitive and label-free detection of the pyocyanin molecule, which is a biomarker of the opportunistic pathogenic bacteria, Pseudomonas aeruginosa. The experimental results showed that the detection limit of pyocyanin with such nanoantenna based biosensor was 335 pM, which is much lower than the clinical range of detection. Thus, fast, sensitive and label-free detection of pyocyanin at ultralow concentration in an infected human body can pave a facile route for early stage warning for severe bacterial infections.

Label-free detection of nosocomial bacteria using a nanophotonic interferometric biosensor

Nosocomial infections are a major concern at the worldwide level. Early and accurate identification of nosocomial pathogens is crucial to provide timely and adequate treatment. A prompt response also prevents the progression of the infection to life-threatening conditions, such as septicemia or generalized bloodstream infection. We have implemented two highly sensitive methodologies using an ultrasensitive photonic biosensor based on a bimodal waveguide interferometer (BiMW) for the fast detection of Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), two of the most prevalent bacteria associated with nosocomial infections. For that, we have developed a biofunctionalization strategy based on the use of a PEGylated silane (silane-PEG-COOH) which provides a highly resistant and bacteria-repelling surface, which is crucial to specifically detect each bacterium. Two different biosensor assays have been set under standard buffer conditions: one based on a specific direct immunoassay employing polyclonal antibodies for the detection of P. aeruginosa and another one employing aptamers for the direct detection of MRSA. The biosensor immunoassay for P. aeruginosa is fast (it only takes 12 min) and specific and has experimentally detected concentrations down to 800 cfu mL-1 (cfu: colony forming unit). The second one relies on the use of an aptamer that specifically detects penicillin-binding protein 2a (PBP2a), a protein only expressed in the MRSA mutant, providing a photonic biosensor with the ability to identify the resistant pathogen MRSA and differentiate it from methicillin-susceptible S. aureus (MSSA). Direct, label-free, and selective detection of whole MRSA bacteria has been achieved, making possible the direct detection of also 800 cfu mL-1. According to the signal-to-noise (S/N) ratio of the device, a theoretical limit of detection (LOD) of around 49 and 29 cfu mL-1 was estimated for P. aeruginosa and MRSA, respectively. Both results obtained under standard conditions reveal the great potential this interferometric biosensor device has as a versatile and specific tool for bacterial detection and quantification, providing a rapid method for the identification of nosocomial pathogens within the clinical requirements of sensitivity for the diagnosis of infections.

Electrochemical Detection of Pyocyanin as a Biomarker for Pseudomonas aeruginosa: A Focused Review

Pseudomonas aeruginosa (PA) is a pathogen that is recognized for its advanced antibiotic resistance and its association with serious diseases such as ventilator-associated pneumonia and cystic fibrosis. The ability to rapidly detect the presence of pathogenic bacteria in patient samples is crucial for the immediate eradication of the infection. Pyocyanin is one of PA’s virulence factors used to establish infections. Pyocyanin promotes virulence by interfering in numerous cellular functions in host cells due to its redox-activity. Fortunately, the redox-active nature of pyocyanin makes it ideal for detection with simple electrochemical techniques without sample pretreatment or sensor functionalization. The previous decade has seen an increased interest in the electrochemical detection of pyocyanin either as an indicator of the presence of PA in samples or as a tool for quantifying PA virulence. This review provides the first overview of the advances in electrochemical detection of pyocyanin and offers an input regarding the future directions in the field.

Redox Electrochemistry to Interrogate and Control Biomolecular Communication

Cells often communicate by the secretion, transport, and perception of molecules. Information conveyed by molecules is encoded, transmitted, and decoded by cells within the context of the prevailing microenvironments. Conversely, in electronics, transmission reliability and message validation are predictable, robust, and less context dependent. In turn, many transformative advances have resulted by the formal consideration of information transfer. One way to explore this potential for biological systems is to create bio-device interfaces that facilitate bidirectional information transfer between biology and electronics. Redox reactions enable this linkage because reduction and oxidation mediate communication within biology and can be coupled with electronics. By manipulating redox reactions, one is able to combine the programmable features of electronics with the ability to interrogate and modulate biological function. In this review, we examine methods to electrochemically interrogate the various components of molecular communication using redox chemistry and to electronically control cell communication using redox electrogenetics.

Exploring community evolutionary characteristics of microbial populations with supplementation of Camellia green tea extracts in microbial fuel cells

This first-attempt study deciphered combined characteristics of species evolution and bioelectricity generation of microbial community in microbial fuel cells (MFCs) supplemented with Camellia green tea (GT) extracts for biomass energy extraction. Prior studies indicated that polyphenols-rich extracts as effective redox mediators (RMs) could exhibit significant electrochemical activities to enhance power generation in MFCs. However, the supplementation of Camellia GT extract obtained at room temperature with significant redox capabilities into MFCs unexpectedly exhibited obvious inhibitory effect towards power generation. This systematic study indicated that the presence of antimicrobial components (especially catechins) in GT extract might significantly alter the distribution of microbial community, in particular a decrease of microbial diversity and evenness. For practical applications to different microbial systems, pre-screening criteria of selecting biocompatible RMs should not only consider their promising redox capabilities (abiotic), but also possible inhibitory potency (biotic) to receptor microbes. Although Camellia tea extract was well-characterized as GRAS energy drink, some contents (e.g., catechins) may still express inhibition towards organisms and further assessment upon biotoxicity may be inevitably required for practice.

Emerging Technologies for the Electrochemical Detection of Bacteria

Infections are a huge economic liability to the health care system, although real-time detection can allow early treatment protocols to avoid some of this cost and patient morbidity and mortality. Pseudomonas aeruginosa (PA) is a drug-resistant gram-negative bacterium found ubiquitously in clinical settings, accounting for up to 27% of hospital acquired infections. PA secretes a vast array of molecules, ranging from secondary metabolites to quorum sensing molecules, of which many can be exploited to monitor bacterial presence. In addition to electrochemical immunoassays to sense bacteria via antigen-antibody interactions, PA pertains a distinct redox-active virulence factor called pyocyanin (PYO), allowing a direct electrochemical detection of the bacteria. There has been a surge of publications relating to the electrochemical tracing of PA via a myriad of novel biosensing techniques, materials, and methodologies. In addition to indirect methods, research approaches where PYO has been sensitively detected using surface modified electrodes are reviewed and compared with conventional PA-sensing methodologies. This review aims at presenting indirect and direct electrochemical methods currently developed using various surface modified electrodes, materials, and electrochemical configurations on their electrocatalytic effects on sensing of PA and in particular PYO.

Phenazines as potential biomarkers of Pseudomonas aeruginosa infections: synthesis regulation, pathogenesis and analytical methods for their detection

Infectious diseases are still a worldwide important problem. This fact has led to the characterization of new biomarkers that would allow an early, fast and reliable diagnostic and targeted therapy. In this context, Pseudomonas aeruginosa can be considered one of the most threatening pathogens since it causes a wide range of infections, mainly in patients that suffer other diseases. Antibiotic treatment is not trivial given the incidence of resistance processes and the fewer new antibiotics that are placed on the market. With this scenario, relevant quorum sensing (QS) molecules that regulate the secretion of virulence factors and biofilm formation can play an important role in diagnostic and therapeutic issues. In this review, we have focused our attention on phenazines, as possible new biomarkers. They are pigmented metabolites that are produced by diverse bacteria, characterized for presenting unique redox properties. Phenazines are involved in virulence, competitive fitness and are an essential component of the bacterial QS system. Here we describe their role in bacterial pathogenesis and we revise phenazine production regulation systems. We also discuss phenazine levels previously reported in bacterial isolates and in clinical samples to evaluate them as putative good candidates to be used as P. aeruginosa infection biomarkers. Moreover we deeply go through all analytical techniques that have been used for their detection and also new approaches are discussed from a critical point. Graphical abstract.

Development of a longevous two-species biophotovoltaics with constrained electron flow

Microbial biophotovoltaics (BPV) offers a biological solution for renewable energy production by using photosynthetic microorganisms as light absorbers. Although abiotic engineering approaches, e.g., electrode modification and device optimization, can enhance the electrochemical communication between living cells and electrodes, the power densities of BPV are still low due to the weak exoelectrogenic activity of photosynthetic microorganisms. Here, we develop a BPV based on a D-lactate mediated microbial consortium consisting of photosynthetic cyanobacteria and exoelectrogenic Shewanella. By directing solar energy from photons to D-lactate, then to electricity, this BPV generates a power density of over 150 mW·m^-2 in a temporal separation setup. Furthermore, a spatial-temporal separation setup with medium replenishment enables stable operation for over 40 days with an average power density of 135 mW·m^-2. These results demonstrate the electron flow constrained microbial consortium can facilitate electron export from photosynthetic cells and achieve an efficient and durable power output.

Synergic action of thermosensitive hydrogel and Au/Ag nanoalloy for sensitive and selective detection of pyocyanin

The rapid detection of bacterial strains has become a major topic thoroughly discussed across the biomedical field. Paired with the existence of nosocomial pathogen agents that imply extreme medical and financial challenges throughout diagnosis and treatment, the development of rapid and easy-to-use sensing devices has gained an increased amount of attention. Moreover, antibiotic resistance considered by World Health Organization as one of the "biggest threats to global health, food security, and development today" enables this topic as high priority. Pseudomonas aeruginosa, one of the most ubiquitous bacterial strains, has various quorum-sensing systems that are a direct cause of their virulence. One of them is represented by pyocyanin, a blue pigment with electroactive properties that is synthesized from early stages of bacterial colonization. Thus, the sensitive detection of this biomarker could enable a personalized and efficient therapy. It was achieved with the development of an electrochemical sensor based on a thermosensitive polymer, modified with Au/Ag nanoalloy for the rapid and accurate detection of pyocyanin, a virulence biomarker of Pseudomonas aeruginosa. The sensor displayed a linear range from 0.12 to 25 μM, and a limit of detection of 0.04 μM (signal/noise = 3). It was successfully tested in real samples spiked with the target analyte without any pretreatment other than a dilution step. The detection of pyocyanin with high recovery in whole blood in a time frame of 5-10 min from the moment of collection was performed with this electrochemical sensor. Graphical abstract.

Detection of Pyocyanin Using a New Biodegradable SERS Biosensor Fabricated Using Gold Coated Zein Nanostructures Further Decorated with Gold Nanoparticles

In this paper, a biodegradable gold coated zein film surface enhanced Raman spectroscopy (SERS) platform, with gold nanoparticles (AuNPs) deposited on the surface to further enhance the Raman signal, was used to detect pyocyanin (PYO), the toxin secreted by Pseudomonas aeruginosa. An inverted pyramid structure imprinted on a zein film and gold coated during the transfer process was further improved with the deposition and fixing of gold nanoparticles, which resulted in enhancement of the SERS signal by approximately a decade. This new platform served as a lab-on-a-chip sensor to enable the sensitive and rapid detection of PYO in drinking water. The size, distribution, and morphology of the zein film nanostructures including the presence and distribution of gold nanoparticles were characterized by scanning electron microscopy (SEM). The new zein-based platform has the advantage of being largely biodegradable compared with commercial silicon- or glass-based platforms. The limit of detection for PYO using the newly developed zein-based SERS sensor platform was calculated as 25 μM, considerably lower than the concentration of PYO in the blood of people with cystic fibrosis which has been reported to be 70 μM.

Incorporating microbial community data with machine learning techniques to predict feed substrates in microbial fuel cells

The complicated interactions that occur in mixed-species biotechnologies, including biosensors, hinder chemical detection specificity. This lack of specificity limits applications in which biosensors may be deployed, such as those where an unknown feed substrate must be determined. The application of genomic data and well-developed data mining technologies can overcome these limitations and advance engineering development. In the present study, 69 samples with three different substrate types (acetate, carbohydrates and wastewater) collected from various laboratory environments were evaluated to determine the ability to identify feed substrates from the resultant microbial communities. Six machine learning algorithms with four different input variables were trained and evaluated on their ability to predict feed substrate from genomic datasets. The highest accuracies of 93 ± 6% and 92 ± 5% were obtained using NNET trained on datasets classified at the phylum and family taxonomic level, respectively. These accuracies corresponded to kappa values of 0.87 ± 0.10, 0.86 ± 0.09, respectively. Four out of six of the algorithms used maintained accuracies above 80% and kappa values higher than 0.66. Different sequencing method (Roche 454 or Illumina sequencing) did not affect the accuracies of all algorithms, except SVM at the phylum level. All algorithms trained on NMDS-compressed datasets obtained accuracies over 80%, while models trained on PCoA-compressed datasets presented a 10-30% reduction in accuracy. These results suggest that incorporating microbial community data with machine learning algorithms can be used for the prediction of feed substrate and for the potential improvement of MFC-based biosensor signal specificity, providing a new use of machine learning techniques that has substantial practical applications in biotechnological fields.

A mediator-free whole-cell electrochemical biosensing system for sensitive assessment of heavy metal toxicity in water

A bioelectrochemical sensing system (BES) based on electroactive bacteria (EAB) has been used as a new and promising tool for water toxicity assessment. However, most EAB can reduce heavy metals, which usually results in low toxicity response. Herein, a starvation pre-incubation strategy was developed which successfully avoided the metal reduction during the toxicity sensing period. By integrating this starvation pre-incubation procedure with the amperometric BES, a sensitive, robust and mediator-free biosensing method for heavy metal toxicity assessment was developed. Under the optimized conditions, the IC50 (half maximal inhibitory concentration) values for Cu²⁺, Ni²⁺, Cd²⁺, and Cr⁶⁺ obtained were 0.35, 3.49, 6.52, 2.48 mg L^-1, respectively. The measurement with real water samples also suggested this method was reliable for practical application. This work demonstrates that it is feasible to use EAB for heavy metal toxicity assessment and provides a new tool for water toxicity warning.

On-going applications of Shewanella species in microbial electrochemical system for bioenergy, bioremediation and biosensing

Microbial electrochemical system (MES) has attracted ever-growing interest as a promising platform for renewable energy conversion and bioelectrochemical remediation. Shewanella species, the dissimilatory metal reduction model bacteria with versatile extracellular electron transfer (EET) strategies, are the well-received microorganisms in diverse MES devices for various practical applications as well as microbial EET mechanism investigation. Meanwhile, the available genomic information and the unceasing established gene-editing toolbox offer an unprecedented opportunity to boost the applications of Shewanella species in MES. This review thoroughly summarizes the status quo of the applications of Shewanella species in microbial fuel cells for bioelectricity generation, microbial electrosynthesis for biotransformation of valuable chemicals and bioremediation of environment-hazardous pollutants with synoptical discussion on their EET mechanism. Recent advances in rational design and genetic engineering of Shewanella strains for either promoting the MES performance or broadening their applications are surveyed. Moreover, some emerging applications beyond electricity generation, such as biosensing and biocomputing, are also documented. The challenges and perspectives for Shewanella-based MES are also discussed elaborately for the sake of not only discovering new scientific lights on microbial extracellular respiratory but also propelling practical applications.

Bioelectrochemical biosensor for water toxicity detection: generation of dual signals for electrochemical assay confirmation

Toxicity assessment of water is of great important to the safety of human health and to social security because of more and more toxic compounds that are spilled into the aquatic environment. Therefore, the development of fast and reliable toxicity assessment methods is of great interest and attracts much attention. In this study, by using the electrochemical activity of Shewanella oneidensis MR-1 cells as the toxicity indicator, 3,5-dichlorophenol (DCP) as the model toxic compound, a new biosensor for water toxicity assessment was developed. Strikingly, the presence of DCP in the water significantly inhibited the maximum current output of the S. oneidensis MR-1 in a three-electrode system and also retarded the current evolution by the cells. Under the optimized conditions, the maximum current output of the biosensor was proportional to the concentration of DCP up to 30 mg/L. The half maximal inhibitory concentration of DCP determined by this biosensor is about 14.5 mg/L. Furthermore, simultaneous monitoring of the retarded time (Δt) for current generation allowed the identification of another biosensor signal in response to DCP which could be employed to verify the electrochemical result by dual confirmation. Thus, the present study has provided a reliable and promising approach for water quality assessment and risk warning of water toxicity.