Research progress of metal-organic framework nanozymes in bacterial sensing, detection, and treatment

The high efficiency and specificity of enzymes make them play an important role in life activities, but the high cost, low stability and high sensitivity of natural enzymes severely restrict their application. In recent years, nanozymes have become convincing alternatives to natural enzymes, finding utility across diverse domains, including biosensing, antibacterial interventions, cancer treatment, and environmental preservation. Nanozymes are characterized by their remarkable attributes, encompassing high stability, cost-effectiveness and robust catalytic activity. Within the contemporary scientific landscape, metal-organic frameworks (MOFs) have garnered considerable attention, primarily due to their versatile applications, spanning catalysis. Notably, MOFs serve as scaffolds for the development of nanozymes, particularly in the context of bacterial detection and treatment. This paper presents a comprehensive review of recent literature pertaining to MOFs and their pivotal role in bacterial detection and treatment. We explored the limitations and prospects for the development of MOF-based nanozymes as a platform for bacterial detection and therapy, and anticipate their great potential and broader clinical applications in addressing medical challenges.

Diagnosis and Therapeutic Strategies Based on Nucleic Acid Aptamers Selected against Pseudomonas aeruginosa: The Challenge of Cystic Fibrosis

Antimicrobial resistance (AMR) is a rapidly spreading global health problem, and approximately five million deaths associated with AMR pathogens were identified prior to the COVID-19 pandemic. Pseudomonas aeruginosa has developed increasing AMR, and in patients with cystic fibrosis (CF) colonized by this bacterium, rare phenotypes have emerged that complicate the diagnosis and treatment of the hosts, in addition to multiple associated "epidemic strains" with high morbidities and mortalities. The conjugation of aptamers with fluorochromes or nanostructures has allowed the design of new identification strategies for Pseudomonas aeruginosa with detection limits of up to 1 cell ⋅ mL-1 , and the synergy of aptamers with antibiotics, antimicrobial peptides and nanostructures has exhibited promising therapeutic qualities. Some selected aptamers against this bacterium have shown intrinsic antimicrobial activity. However, these aptamers have been poorly evaluated in clinical isolates and have shown decreased interactions for CF isolates, demonstrating, in these cases, uncommon phenotypes resulting from the selective qualities of this disease as well as the great adaptive capacity of the pathogen. Therefore, finding an aptamer or set of aptamers that have the ability to recognize strange phenotypes of this bacillus is crucial in the battle against AMR.

Guided mode resonance immunosensor for label-free detection of pathogenic bacteria Pseudomonas aeruginosa

Photonic biosensors are promising platforms for the rapid detection of pathogens with the potential to replace conventional diagnostics based on microbiological culturing methods. Intricately designed sensing elements with robust architectures can offer highly sensitive detection at minimal development cost enabling rapid adoption in low-resource settings. In this work, an optical detection scheme is developed by structuring guided mode resonance (GMR) on a highly stable, transparent silicon nitride (SiN) substrate and further biofunctionalized to identify a specific bacteria Pseudomonas aeruginosa. The resonance condition of the GMR chip is optimized to have relatively high bulk sensitivity with a good quality factor. The biofunctionalization aims at oriented immobilization of specific antibodies to allow maximum bacteria attachment and improved specificity. The sensitivity of the assays is evaluated for clinically relevant concentrations ranging from 102 to 108 CFU/mL. From the calibration curves, the sensitivity of the chip is extracted as 0.134nm/Log10 [concentration], and the detection modality possesses a favorably good limit of detection (LOD) 89 CFU/mL. The use of antibodies as a biorecognition element complemented with a good figure of merit of GMR sensing element allows selective bacteria identification compared to other non-specific pathogenic bacteria that are relevant for testing physiological samples. Our developed GMR biosensor is low-cost, easy to handle, and readily transformable into a portable handheld detection modality for remote usage.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.

Sandwich-Type Electrochemical Aptasensor for Highly Sensitive and Selective Detection of Pseudomonas Aeruginosa Bacteria Using a Dual Signal Amplification Strategy

An electrochemical aptasensor developed to realize the detection of Pseudomonas aeruginosa (P. aeruginosa) bacteria based on a signal amplification strategy. The carbon screen-printed electrode (CSPE) surface was modified by MIL-101(Cr)/Multi-walled carbon nanotubes (MWCNT), which significantly increased the effective surface area of the electrode, thus resulting in further F23 aptamer immobilization at the surface of the modified electrode. As a result, the P. aeruginosa can be efficiently captured onto the surface of the aptasensor. Moreover, aptamer immobilized on the two-dimensional graphitic carbon nitride complex with silver nanoparticles (AgNPs/c-g-C₃N₄/Apt) was used as an electrochemical signal label, connected to P. aeruginosa bacteria at the modified electrode. This strategy increased the aptamer surface density and the sensitivity for detecting P. aeruginosa. Also, the resultant material was thoroughly characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analysis techniques. A highly sensitive voltammetric aptasensor for P. aeruginosa detection was obtained via this strategy at the limit of detection of 1 Colony-forming unit (CFU)/mL (σ = 3). Therefore, this proposed strategy with dual signal amplification can be a promising platform for simple, practical, reliable, and sensitive method for P. aeruginosa.

Pseudomonas aeruginosa detection based on droplets incubation using an integrated microfluidic chip, laser spectroscopy, and machine learning

Pseudomonas aeruginosa is an opportunist pathogen responsible for causing several infections in the human body, especially in patients with weak immune systems. The proposed approach reports a novel pathogens detection system based on cultivating microdroplets and acquiring the scattered light signals from the incubated droplets using a microfluidic device. Initially, the microdroplets were generated and incubated to cultivate bacteria inside the microdroplets. The second part of the microfluidic chip is the detection module, embedded with three optical fibers to connect laser light and photosensors. The incubated droplets were reinjected in the detection module and passed through the laser light. The surrounding photosensors were arranged symmetrically at 45° to the flowing channel for acquiring the scattered light signal. The noise was removed from the acquired data, and time-domain waveform features were evaluated. The acquired features were trained using machine learning classifiers to classify P. aeruginosa. The k-nearest neighbors (KNN) showed superior classification performance with 95.6 % accuracy among other classifiers, including logistic regression (LR), support vector machines (SVM), and naïve Bayes (NB). The proposed research was performed to validate the method for pathogens detection with a concentration of 10⁵ CFU/mL. The total duration of 6 h is required to test the sample, including five hours for droplets incubation and one hour for sample preparation and detection using light scattering module. The results indicate that acquiring the light scattering patterns from incubated droplets can detect P. aeruginosa using machine learning classification. The proposed system is anticipated to be helpful as a rapid device for diagnosing pathogenic infections.

Thermal Pyocyanin Sensor Based on Molecularly Imprinted Polymers for the Indirect Detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a ubiquitous multi-drug-resistant bacterium, capable of causing serious illnesses and infections. This research focuses on the development of a thermal sensor for the indirect detection of P. aeruginosa infection using molecularly imprinted polymers (MIPs). This was achieved by developing MIPs for the detection of pyocyanin, the main toxin secreted by P. aeruginosa. To this end, phenazine was used as a dummy template, evaluating several polymeric compositions to achieve a selective MIP for pyocyanin recognition. The sensitivity of the synthesized MIPs was investigated by UV-vis analysis, with the best composition having a maximum rebinding capacity of 30 μmol g^-1 and an imprinting factor (IF) of 1.59. Subsequently, the MIP particles were immobilized onto planar aluminum chips using an adhesive layer, to perform thermal resistance measurements at clinically relevant concentrations of pyocyanin (1.4-9.8 μM), achieving a limit of detection (LoD) of 0.347 ± 0.027 μM. The selectivity of the sensor was also scrutinized by subjecting the receptor to potential interferents. Furthermore, the rebinding was demonstrated in King's A medium, highlighting the potential of the sensor for the indirect detection of P. aeruginosa in complex fluids. The research culminates in the demonstration of the MIP-based sensor's applicability for clinical diagnosis. To achieve this goal, an experiment was performed in which the sensor was exposed to pyocyanin-spiked saliva samples, achieving a limit of detection of 0.569 ± 0.063 μM and demonstrating that this technology is suitable to detect the presence of the toxin even at the very first stage of its production.

Flow cytometry-based rapid detection of Staphylococcus aureus and Pseudomonas aeruginosa using fluorescent antibodies

Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) are major pathogens frequently detected in food and beverage poisoning, and persistent infections. Therefore, the development of a rapid method that can detect these pathogens before serious multiplication is required. In this study, we established a flow cytometry (FCM)-based detection method that allows rapid acquisition of cell populations in fluid samples by using a fluorescent antibody against S. aureus or P. aeruginosa. Using this method, we detected these pathogens with a 10³ to 10⁵ CFU order of limit of detection value within 1 hour. The FCM-based method for the detection of S. aureus and P. aeruginosa offers the possibility of high-throughput analysis of pathogens in food, environmental, and clinical sources.

Generation of a recombinant antibody for sensitive detection of Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is a major pathogen that causes nosocomial infections and often exhibits antibiotic resistance. Therefore, the development of an accurate method for detecting P. aeruginosa is required to control P. aeruginosa-related outbreaks. In this study, we established an enzyme-linked immunosorbent assay method for the sensitive detection of three P. aeruginosa strains, UCBPP PA14, ATCC 27853, and multidrug-resistant ATCC BAA-2108. We produced a recombinant antibody (rAb) against P. aeruginosa V‐antigen (PcrV), which is a needle tip protein of the type III secretion system of P. aeruginosa using mammalian cells with high yield and purity, and confirmed its P. aeruginosa binding efficiency. The rAb was paired with commercial anti-P. aeruginosa Ab for a sandwich ELISA, resulting in an antigen-concentration-dependent response with a limit of detection value of 230 CFU/mL. These results suggest that the rAb produced herein can be used for the sensitive detection of P. aeruginosa with a wide range of applications in clinical diagnosis and point-of-care testing.

Pseudomonas aeruginosa Detection Using Conventional PCR and Quantitative Real-Time PCR Based on Species-Specific Novel Gene Targets Identified by Pangenome Analysis

Mining novel specific molecular targets and establishing efficient identification methods are significant for detecting Pseudomonas aeruginosa, which can enable P. aeruginosa tracing in food and water. Pangenome analysis was used to analyze the whole genomic sequences of 2017 strains (including 1,000 P. aeruginosa strains and 1,017 other common foodborne pathogen strains) downloaded from gene databases to obtain novel species-specific genes, yielding a total of 11 such genes. Four novel target genes, UCBPP-PA14_00095, UCBPP-PA14_03237, UCBPP-PA14_04976, and UCBPP-PA14_03627, were selected for use, which had 100% coverage in the target strain and were not present in nontarget bacteria. PCR primers (PA1, PA2, PA3, and PA4) and qPCR primers (PA12, PA13, PA14, and PA15) were designed based on these target genes to establish detection methods. For the PCR primer set, the minimum detection limit for DNA was 65.4 fg/μl, which was observed for primer set PA2 of the UCBPP-PA14_03237 gene. The detection limit in pure culture without pre-enrichment was 10⁵ colony-forming units (CFU)/ml for primer set PA1, 10³ CFU/ml for primer set PA2, and 10⁴ CFU/ml for primer set PA3 and primer set PA4. Then, qPCR standard curves were established based on the novel species-specific targets. The standard curves showed perfect linear correlations, with R² values of 0.9901 for primer set PA12, 0.9915 for primer set PA13, 0.9924 for primer set PA14, and 0.9935 for primer set PA15. The minimum detection limit of the real-time PCR (qPCR) assay was 10² CFU/ml for pure cultures of P. aeruginosa. Compared with the endpoint PCR and traditional culture methods, the qPCR assay was more sensitive by one or two orders of magnitude. The feasibility of these methods was satisfactory in terms of sensitivity, specificity, and efficiency after evaluating 29 ready-to-eat vegetable samples and was almost consistent with that of the national standard detection method. The developed assays can be applied for rapid screening and detection of pathogenic P. aeruginosa, providing accurate results to inform effective monitoring measures in order to improve microbiological safety.

Applications of Nanozymology in the Detection and Identification of Viral, Bacterial and Fungal Pathogens

Nanozymes are synthetic nanoparticulate materials that mimic the biological activities of enzymes by virtue of their surface chemistry. Enzymes catalyze biological reactions with a very high degree of specificity. Examples include the horseradish peroxidase, lactate, glucose, and cholesterol oxidases. For this reason, many industrial uses of enzymes outside their natural environments have been developed. Similar to enzymes, many industrial applications of nanozymes have been developed and used. Unlike the enzymes, however, nanozymes are cost-effectively prepared, purified, stored, and reproducibly and repeatedly used for long periods of time. The detection and identification of pathogens is among some of the reported applications of nanozymes. Three of the methodologic milestones in the evolution of pathogen detection and identification include the incubation and growth, immunoassays and the polymerase chain reaction (PCR) strategies. Although advances in the history of pathogen detection and identification have given rise to novel methods and devices, these are still short of the response speed, accuracy and cost required for point-of-care use. Debuting recently, nanozymology offers significant improvements in the six methodological indicators that are proposed as being key in this review, including simplicity, sensitivity, speed of response, cost, reliability, and durability of the immunoassays and PCR strategies. This review will focus on the applications of nanozymes in the detection and identification of pathogens in samples obtained from foods, natural, and clinical sources. It will highlight the impact of nanozymes in the enzyme-linked immunosorbent and PCR strategies by discussing the mechanistic improvements and the role of the design and architecture of the nanozyme nanoconjugates. Because of their contribution to world health burden, the three most important pathogens that will be considered include viruses, bacteria and fungi. Although not quite seen as pathogens, the review will also consider the detection of cancer cells and helminth parasites. The review leaves very little doubt that nanozymology has introduced remarkable advances in enzyme-linked immunosorbent assays and PCR strategies for detecting these five classes of pathogens. However, a gap still exists in the application of nanozymes to detect and identify fungal pathogens directly, although indirect strategies in which nanozymes are used have been reported. From a mechanistic point of view, the nanozyme technology transfer to laboratory research methods in PCR and enzyme-linked immunosorbent assay studies, and the point-of-care devices such as electronic biosensors and lateral flow detection strips, that is currently taking place, is most likely to give rise to no small revolution in each of the six methodological indicators for pathogen detection and identification. While the evidence of widespread research reports, clinical trials and point-of-care device patents support this view, the gaps that still exist point to a need for more basic research studies to be conducted on the applications of nanozymology in pathogen detection and identification. The multidisciplinary nature of the research on the application of nanozymes in the detection and identification of pathogens requires chemists and physicists for the design, fabrication, and characterization of nanozymes; microbiologists for the design, testing and analysis of the methodologies, and clinicians or clinical researchers for the evaluation of the methodologies and devices in the clinic. Many reports have also implicated required skills in mathematical modelling, and electronic engineering. While the review will conclude with a synopsis of the impact of nanozymology on the detection and identification of viruses, bacteria, fungi, cancer cells, and helminths, it will also point out opportunities that exist in basic research as well as opportunities for innovation aimed at novel laboratory methodologies and devices. In this regard there is no doubt that there are numerous unexplored research areas in the application of nanozymes for the detection of pathogens. For example, most research on the applications of nanozymes for the detection and identification of fungi is so far limited only to the detection of mycotoxins and other chemical compounds associated with fungal infection. Therefore, there is scope for exploration of the application of nanozymes in the direct detection of fungi in foods, especially in the agricultural production thereof. Many fungal species found in seeds severely compromise their use by inactivating the germination thereof. Fungi also produce mycotoxins that can severely compromise the health of humans if consumed.

Spectroscopic ellipsometry methods for brevetoxin detection

The spectroscopic ellipsometry (SE), and attenuated internal reflection spectroscopic ellipsometry (TIRE) are promising methods in label-free biosensing applications. An ellipsometer running under surface plasmon resonance (SPR) conditions has unique advantages over other SPR-based methods in terms of sensitivity and real-time/label-free measurement capability. In this study, both SE and TIRE-based brevetoxin B (BTX) sensors were developed using two anti-BTX aptamers reported before. A new aptamer sequence was also derived from these two antiBTX aptamers using predictive modeling tools and an exclusion method. All three antiBTX aptamers' analytical performances were quite competitive in terms of both detecting range and detection limits. However, the selectivity of the previously reported aptamers against analogs of BTX was poor at low detection ranges, especially for okadaic acid. Furthermore, the selectivity of the derived aptamer was lower than its predecessors. The sensors were capable of detecting BTX in the range of 0.05 nM-1600 nM in the TIRE and 0.5 nM-2000 nM in the SE configuration. The detection limits of the sensors were 1.48 nM (1.32 ng/mL) and 0.80 nM (0.72 ng/mL) for SE and TIRE configurations, respectively. Both configurations have been used successfully to detect BTX standards spiked into real fish and shrimp samples.

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.

Rapid detection of Pseudomonas aeruginosa based on lab-on-a-chip platform using immunomagnetic separation, light scattering, and machine learning

The rapid detection of the pathogenic bacteria in patient samples is crucial to expedient patient care. The proposed approach reports the development of a novel lab-on-a-chip device for the rapid detection of P. aeruginosa based on immunomagnetic separation, optical scattering, and machine learning. The immunomagnetic particles with a diameter of 5 μm were synthesized for isolating P. aeruginosa from the test sample. A microfluidic chip was fabricated, and three optical fibers were embedded for connecting a laser light and two photodetectors. The laser light was pointed towards the channel to pass light through the sample. A pair of photodetectors via optical fibers were arranged symmetrically at 45° to the channel. The photodetectors acquired scattered light from the flowing sample and converted the light to an electrical signal. The sample containing immunomagnetic beads linked with bacteria was injected into the microfluidic chip. The optimized conditions for performing the experiments were characterized for real-time detection of P. aeruginosa. The data acquisition system recorded the real-time light scattering from the test sample. After removing noise from the output waveform, five different time-domain statistical features were extracted from each waveform: standard mean, standard variance, skewness, kurtosis, and coefficient of variation. The pathogens classification was performed by training the discrimination model using extracted features based on machine learning algorithms. The support vector machines (SVM) with a sigmoid function kernel showed superior classification performance with 97.9% accuracy among other classifiers, including k-nearest neighbors (KNN), logistic regression (LR), and naïve Bayes (NB). The method can detect P. aeruginosa specifically and quantitatively with a limit of detection of 10² CFU/mL. The device can classify P. aeruginosa within 10 min with a total assay time of 25 min. The device was used to test its ability to detect pathogen from the serum and sputum specimens spiked with 10⁵ CFU/mL concentration of P. aeruginosa. The results indicate that light scattering combined with machine learning can be used to detect P. aeruginosa. The proposed technique is anticipated to be helpful as a rapid device for diagnosing P. aeruginosa related infections.

Modern Analytical Techniques for Detection of Bacteria in Surface and Wastewaters

Contamination of surface waters with pathogens as well as all diseases associated with such events are a significant concern worldwide. In recent decades, there has been a growing interest in developing analytical methods with good performance for the detection of this category of contaminants. The most important analytical methods applied for the determination of bacteria in waters are traditional ones (such as bacterial culturing methods, enzyme-linked immunoassay, polymerase chain reaction, and loop-mediated isothermal amplification) and advanced alternative methods (such as spectrometry, chromatography, capillary electrophoresis, surface-enhanced Raman scattering, and magnetic field-assisted and hyphenated techniques). In addition, optical and electrochemical sensors have gained much attention as essential alternatives for the conventional detection of bacteria. The large number of available methods have been materialized by many publications in this field aimed to ensure the control of water quality in water resources. This study represents a critical synthesis of the literature regarding the latest analytical methods covering comparative aspects of pathogen contamination of water resources. All these aspects are presented as representative examples, focusing on two important bacteria with essential implications on the health of the population, namely Pseudomonas aeruginosa and Escherichia coli.

Fluorescence nucleobase analogue-based strategy with high signal-to-noise ratio for ultrasensitive detection of food poisoning bacteria

We developed a simple and ultrasensitive strategy for the identification of foodborne pathogens utilizing a fluorescent nucleobase analogue [2-aminopurine (2-AP)]-containing split G-quadruplex that binds blocker DNA. Compared to a previous strategy that did not use blocker DNA, this strategy showed a significant increase in the signal-to-noise ratio-by approximately 300%-owing to the displacement of the blocker DNA by the target DNA that induces the formation of an active G-quadruplex structure, thereby leading to a substantial increase in the 2-AP fluorescence signal. The proposed strategy was rationally combined with polymerase chain reaction, which resulted in the successful determination of genomic DNA (within the range of 10-106 copies) derived from the food poisoning bacterium Escherichia coli, with a limit of detection of 5.2 copies and high selectivity. In addition, the practical applicability of this method was demonstrated by analyzing E. coli-spiked lettuce samples.

Clinical analysis of Pseudomonas aeruginosa-positive and -negative green nail syndrome cases: A single center retrospective analysis

Green nail syndrome (GNS) is a paronychial infection mainly due to Pseudomonas aeruginosa, characterized by green discoloration of the nail plate. Although the diagnosis of GNS may be straightforward with its distinctive color change, the clinical management of the disease can be sometimes confusing, especially when the bacterial culture result is inconsistent. There is, however, a paucity of comprehensive reviews regarding the treatment of GNS in the actual clinical setting. In this retrospective review of 34 patients, we found that GNS mostly occurs on a single digit (79.4%) on the big toe or thumb (85.3%) with frequent concurrent fungal infection (67.6%). The prevalence of inconsistent bacterial culture result with no evidence of P. aeruginosa was unexpectedly high (n = 22, 64.7%), in which case coagulase-negative staphylococci were most frequently detected. The P. aeruginosa-negative group did not demonstrate any statistically significant differences compared with the P. aeruginosa-positive group, and it still responded well to the typical topical and/or oral fluoroquinolone treatment. GNS without the evidence of P. aeruginosa may be a more common occurrence than reported in the literature, and it can be managed successfully with the same strategy employed to treat P. aeruginosa-positive cases. It may result from the low detection rate of P. aeruginosa due to the limited sensitivity of the test, or inadequate amount and/or contamination of the sample, warranting close scrutiny by clinicians.

Gold nanoparticle-based immunochromatographic assay for detection Pseudomonas aeruginosa in water and food samples

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An ICA was developed for P. aeruginosa detection.

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The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL.

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The ICA could be applied to detect P. aeruginosa in water and food samples.

Pseudomonas aeruginosa (P. aeruginosa) is the common infection-causing bacterial pathogen. Conventional methods for the detection of P. aeruginosa are time-consuming, and therefore, a more rapid analytical method is required. Here, monoclonal antibodies (Mabs) against P. aeruginosa (CICC 10419) were prepared and based on paired Mabs, an immunochromatographic assay (ICA) was developed. The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL and the linear range of detection was 3.13 × 10⁴-1.0 × 10⁶ CFU/mL. No cross-reactivity was observed when other common Gram-negative and Gram-positive bacteria were used. The analytical performance of the ICA strip indicated that the developed ICA had good specificity and stability. Moreover, the feasibility of the ICA strip was verified by detecting P. aeruginosa (CICC 10419) in spiked water and food samples. The ICA strip could detect samples contaminated with a low-level of P. aeruginosa (CICC 10419) after 8 h enrichment.

Hollow carbon nanocapsules-based nitrogen-doped carbon nanofibers with rosary-like structure as a high surface substrate for impedimetric detection of Pseudomonas aeruginosa

The design of hollow mesoporous carbon-based materials has attracted tremendous attention, due to their sizeable intrinsic cavity to load specific chemical and unique physical/chemical properties in various applications. Herein, we have established an effective strategy for the preparation of novel hollow carbon nanocapsules-based nitrogen-doped carbon nanofibers (CNCNF) with rosary-like structure. By embedding ultrafine hollow carbon nanocapsules into electrospun polyacrylonitrile (PAN) skeleton, the as-designed composite CNFs were carbonized into hierarchical porous CNFs, consisted of interconnected nitrogen-doped hollow carbon nanocapsules. Due to its individual structural properties and unique chemical composition, the performance of CNCNF was evaluated in aptasensor application via the detection of Pseudomonas aeruginosa (PA). Under optimized conditions, the aptasensor based on CNCNF has a detection limit of 1 CFU⋅mL^-1 and a linear range from 10¹ CFU ⋅mL^-1 to 10⁷ CFU ⋅mL^-1 (n = 3). Moreover, the designed aptasensor possesses high sensivity, high selectivity, low detection limit, and high reproducibility. These studies showed that the CNCNF material offers a wide variety of enhanced electrochemical features as an electrode material for aptasensor application.

Conjugation of antibodies and aptamers on nanozymes for developing biosensors

Nanozymes are engineered nanomaterials with enzyme-like activities. Over the past decade, impressive progresses on nanozymes in biosensing have been made due to their unique advantages of high stability, low cost, and easy modification compared to natural enzymes. For many biosensors, it is critical to conjugate nanozymes to affinity ligands such as antibodies and aptamers. Since different nanomaterials have different surface properties, conjugation methods need to be compatible with these properties. In addition, the effect of biomolecules on nanozyme activity needs to be considered. In this review, we first categorized nanozyme-based biosensors into four parts, respectively describing noncovalent and covalent modifications with antibodies and aptamers. Meanwhile, recent advances in antibody and aptamer labeled nanozyme biosensors are summarized, and the methods of their conjugation are further illustrated. Finally, conclusions and future perspectives for the development and application of nanozyme bioconjugates are discussed.

Bacterial Sensing and Biofilm Monitoring for Infection Diagnostics

Recent insights into the rapidly emerging field of bacterial sensing and biofilm monitoring for infection diagnostics are discussed as well as recent key developments and emerging technologies in the field. Electrochemical sensing of bacteria and bacterial biofilm via synthetic, natural, and engineered recognition, as well as direct redox-sensing approaches via algorithm-based optical sensing, and tailor-made optotracing technology are discussed. These technologies are highlighted to answer the very critical question: "how can fast and accurate bacterial sensing and biofilm monitoring be achieved? Following on from that: "how can these different sensing concepts be translated for use in infection diagnostics? A central obstacle to this transformation is the absence of direct and fast analysis methods that provide high-throughput results and bio-interfaces that can control and regulate the means of communication between biological and electronic systems. Here, the overall progress made to date in building such translational efforts at the level of an individual bacterial cell to a bacterial community is discussed.

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.

Electrochemical sensors for rapid diagnosis of pathogens in real time

Microbial infections remain the principal cause for high morbidity and mortality rates. While approximately 1400 human pathogens have been recognized, the majority of healthcare-associated infectious diseases are caused by only a few opportunistic pathogens (e.g., Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli), which are associated with increased antibiotic and antimicrobial resistance. Rapid detection, reliable identification and real-time monitoring of these pathogens remain not only a scientific problem but also a practical challenge of vast importance, especially in tailoring effective treatment strategies. Although the development of vaccinations and antibacterial drug treatments are the leading research, progress, and implementation of early warning, quantitative systems indicative of confirming pathogen presence are necessary. Over the years, various approaches, such as conventional culturing, straining, molecular methods (e.g., polymerase chain reaction and immunological assays), microscopy-based and mass spectrometry techniques, have been employed to identify and quantify pathogenic agents. While being sensitive in some cases, these procedures are costly, time-consuming, mostly qualitative, and are indirect detection methods. A great challenge is therefore to develop rapid, highly sensitive, specific devices with adequate figures of merit to corroborate the presence of microbes and enable dynamic real-time measurements of metabolism. As an alternative, electrochemical sensor platforms have been developed as powerful quantitative tools for label-free detection of infection-related biomarkers with high sensitivity. This minireview is focused on the latest electrochemical-based approaches for pathogen sensing, putting them into the context of standard sensing methods, such as cell culturing, mass spectrometry, and fluorescent-based approaches. Description of the latest, impactful electrochemical sensors for pathogen detection will be presented. Recent breakthroughs will be highlighted, including the use of micro- and nano-electrode arrays for real-time detection of bacteria in polymicrobial infections and microfluidic devices for pathogen separation analysis. We will conclude with perspectives and outlooks to understand shortcomings in designing future sensing schemes. The need for high sensitivity and selectivity, low-cost implementation, fast detection, and screening increases provides an impetus for further development in electrochemical detectors for microorganisms and biologically relevant targets.

A novel enzyme-free electrochemical biosensor for rapid detection of Pseudomonas aeruginosa based on high catalytic Cu-ZrMOF and conductive Super P

Pseudomonas aeruginosa (P. aeruginosa) is one of the most intractable multidrug-resistant bacteria of nosocomial infections. The conventional detection methods for P. aeruginosa are time-consuming or low detection sensitivity. Here, a novel enzyme-free electrochemical biosensor was constructed to detect P. aeruginosa rapidly and sensitively. Firstly, the ZrMOF with large surface area was synthesized, which offers excellent adsorption. Further, it was connected with a specific amount of Cu²⁺ to synthesize Cu-ZrMOF with high catalytic activity. Then the Cu-ZrMOF@Aptamer@DNA nanocomposite was composed and served as the signal probe to catalyse the decomposition of H₂O₂. Moreover, high conductive Super P was introduced to increase the electron transfer for satisfactory detection sensitivity. The proposed biosensor was constructed and used to quantify P. aeruginosa with a wide linearity range of 10-10⁶ CFU mL^-1 and a low limit of detection of 2 CFU mL^-1 (S/N = 3). Compared with conventional methods, the new method of present biosensor is more sensitive, and less time-consuming (only within 120 min). The analytical performance evaluation indicated that the biosensor exhibits good reproducibility and specificity. Finally, the biosensor was successfully applied to quantify P. aeruginosa in spiked urine samples. These results show that the proposed electrochemical biosensor might be a potential laboratory tool for detecting P. aeruginosa in the clinic.

Aptamer-mediated colorimetric and electrochemical detection of Pseudomonas aeruginosa utilizing peroxidase-mimic activity of gold NanoZyme

Despite of various advancements in biosensing, a rapid, accurate, and on-site detection of a bacterial pathogen is a real challenge due to the lack of appropriate diagnostic platforms. To address this unmet need, we herein report an aptamer-mediated tunable NanoZyme sensor for the detection of Pseudomonas aeruginosa, an infectious bacterial pathogen. Our approach exploits the inherent peroxidase-like NanoZyme activity of gold nanoparticles (GNPs) in combination with high affinity and specificity of a Pseudomonas aeruginosa-specific aptamer (F23). The presence of aptamer inhibits the inherent peroxidase-like activity of GNPs by simple adsorption on to the surface of GNPs. However, in the presence of cognate target (P. aeruginosa), owing to the high affinity for P. aeruginosa, the aptamer leaves the GNP surface, allowing GNPs to resume their peroxidase-like activity, resulting in oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). As TMB is an electrochemically active species, we have been able to translate the NanoZyme-based method into an ultrasensitive electrochemical assay using disposable carbon screen-printed electrode. This approach is highly sensitive and allows us to rapidly detect P. aeruginosa with a low-end detection limit of ~ 60 CFU/mL in water within 10 min. This generic aptamer-NanoZyme-based electrochemical sensing strategy may, in principle, be applicable for the detection of various other bacterial pathogens.