Uniform fluorescent nanobioprobes for pathogen detection

Nanomaterials-based electrochemical biosensors for diagnosis of COVID-19

Since the outbreak of corona virus disease 2019 (COVID-19), this pandemic has caused severe death and infection worldwide. Owing to its strong infectivity, long incubation period, and nonspecific symptoms, the early diagnosis is essential to reduce risk of the severe illness. The electrochemical biosensor, as a fast and sensitive technique for quantitative analysis of body fluids, has been widely studied to diagnose different biomarkers caused at different infective stages of COVID-19 virus (SARS-CoV-2). Recently, many reports have proved that nanomaterials with special architectures and size effects can effectively promote the biosensing performance on the COVID-19 diagnosis, there are few comprehensive summary reports yet. Therefore, in this review, we will pay efforts on recent progress of advanced nanomaterials-facilitated electrochemical biosensors for the COVID-19 detections. The process of SARS-CoV-2 infection in humans will be briefly described, as well as summarizing the types of sensors that should be designed for different infection processes. Emphasis will be supplied to various functional nanomaterials which dominate the biosensing performance for comparison, expecting to provide a rational guidance on the material selection of biosensor construction for people. Finally, we will conclude the perspective on the design of superior nanomaterials-based biosensors facing the unknown virus in future.

Biosynthesis of NIR-II Ag2 Se Quantum Dots with Bacterial Catalase for Photoacoustic Imaging and Alleviating-Hypoxia Photothermal Therapy

Developing the second near-infrared (NIR-II) photoacoustic (PA) agent is of great interest in bioimaging. Ag2 Se quantum dots (QDs) are one kind of potential probe for applications in NIR-II photoacoustic imaging (PAI). However, the surfaces with excess anions of Ag2 Se QDs, which increase the probability of nonradiative transitions of excitons benefiting PA imaging, are not conducive to binding electron donor ligands for potential biolabeling and imaging. In this study, Staphylococcus aureus (S. aureus) cells are driven for the biosynthesis of Ag2 Se QDs with catalase (CAT). Biosynthesized Ag2 Se (bio-Ag2 Se-CAT) QDs are produced in Se-enriched environment of S. aureus and have a high Se-rich surface. The photothermal conversion efficiency of bio-Ag2 Se-CAT QDs at 808 and 1064 nm is calculated as 75.3% and 51.7%, respectively. Additionally, the PA signal responsiveness of bio-Ag2 Se-CAT QDs is ≈10 times that of the commercial PA contrast agent indocyanine green. In particular, the bacterial CAT is naturally attached to bio-Ag2 Se-CAT QDs surface, which can effectively relieve tumor hypoxia. The bio-Ag2 Se-CAT QDs can relieve heat-initiated oxidative stress while undergoing effective photothermal therapy (PTT). Such biosynthesis method of NIR-II bio-Ag2 Se-CAT QDs opens a new avenue for developing multifunctional nanomaterials, showing great promise for PAI, hypoxia alleviation, and PTT.

In-situ synthesis of quantum dots in the nucleus of live cells

The cell nucleus is the main site for the storage and replication of genetic material, and the synthesis of substances in the nucleus is rhythmic, regular and strictly regulated by physiological processes. However, whether exogenous substances, such as nanoparticles, can be synthesized in situ in the nucleus of live cells has not been reported. Here, we have achieved in-situ synthesis of CdSxSe1-x quantum dots (QDs) in the nucleus by regulation of the glutathione (GSH) metabolic pathway. High enrichment of GSH in the nucleus can be accomplished by the addition of GSH with the help of the Bcl-2 protein. Then, high-valence Se is reduced to low-valence Se by glutathione-reductase-catalyzed GSH, and interacts with the Cd precursor formed through Cd and thiol-rich proteins, eventually generating QDs in the nucleus. Our work contributes to a new understanding of the syntheses of substances in the cell nucleus and will pave the way for the development of advanced 'supercells'.

Aggregation-Induced Emission-Based Chemiluminescence Systems in Biochemical Analysis and Disease Theranostics

Chemiluminescence (CL) is of great significance in biochemical analysis and imaging due to its high sensitivity and lack of need for external excitation. In this review, we summarized the recent progress of AIE-based CL systems, including their working mechanisms and applications in biochemical analysis, bioimaging, and disease diagnosis and treatment. In ion and molecular detection, CL shows high selectivity and high sensitivity, especially in the detection of dynamic reactive oxygen species (ROS). Further, the integrated NIR-CL single-molecule system and nanostructural CL platform harnessing CL resonance energy transfer (CRET) have remarkable advantages in long-term imaging with superior capability in penetrating deep tissue depth and high signal-to-noise ratio, and are promising in the applications of in vivo imaging and image-guided disease therapy. Finally, we summarized the shortcomings of the existing AIE-CL system and provided our perspective on the possible ways to develop more powerful CL systems in the future. It can be highly expected that these promoted CL systems will play bigger roles in biochemical analysis and disease theranostics.

Boosting SARS-CoV-2 Enrichment with Ultrasmall Immunomagnetic Beads Featuring Superior Magnetic Moment

The isolation and enrichment efficiency of SARS-CoV-2 virus in complex biological environments is often relatively low, presenting challenges in direct detection and an increased risk of false negatives, particularly during the early stages of infection. To address this issue, we have developed a novel approach using ultrasmall magnetosome-like nanoparticles (≤10 nm) synthesized via biomimetic mineralization of the Mms6 protein derived from magnetotactic bacteria. These nanoparticles are surface-functionalized with hydrophilic carboxylated polyethylene glycol (mPEG2000-COOH) to enhance water solubility and monodispersity. Subsequently, they are coupled with antibodies targeting the receptor-binding domain (RBD) of the virus. The resulting magnetosome-like immunomagnetic beads (Mal-IMBs) exhibit high magnetic responsiveness comparable to commercial magnetic beads, with a saturation magnetization of 90.6 emu/g. Moreover, their smaller particle size provides a significant advantage by offering a higher specific surface area, allowing for a greater number of RBD single-chain fragment variable (RBD-scFv) antibodies to be coupled, thereby enhancing immune capture ability and efficiency. To validate the practicality of Mal-IMBs, we evaluated their performance in recognizing the RBD antigens, achieving a maximum capture ability of 83 μg/mg per unit mass. Furthermore, we demonstrated the binding capability of Mal-IMBs to SARS-CoV-2 pseudovirus using fluorescence microscopy. The Mal-IMBs effectively enriched the pseudovirus at a low copy concentration of 70 copies/mL. Overall, the small Mal-IMB exhibited excellent magnetic responsiveness and binding efficiency. By employing a multisite virus binding mechanism, it significantly improves the enrichment and separation of SARS-CoV-2 in complex environments, facilitating rapid detection of COVID-19 and contributing to effective measures against its spread.

Biosynthesis of uniform fluorescent-stable telluride quantum dots in Escherichia coli and its detection of Fe3+ in water

Quantum dots (QDs) containing zinc (Zn) and tellurium (Te) have low toxicity and excellent optoelectronic properties, which make them ideal fluorescent probes for use in environmental monitoring. However, their size/shape distribution synthesized by existing methods is not as good as that of other nanoparticles, thus limiting their application. Exploring whether this kind of QD can be biosynthesized and whether it can act as a nanoprobe are favorable attempts to expand the synthesis method and the application of QDs. Telluride QDs were biosynthesized in Escherichia coli cells. The nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and inductively coupled plasma-atomic emission spectrometry (ICP‒AES), indicating that they were Zn₃STe₂ QDs. The QDs were monodispersed, spherical and fluorescently stable, with a uniform particle size of 3.05 ± 0.48 nm. The biosynthesis conditions of the QDs, including substrate concentrations and their process time, were optimized respectively. It was verified that the cysE and cysK genes were involved in the biosynthesis of telluride QDs. The biosynthesis ability of the QDs was improved by knocking out the tehB gene and overexpressing the pckA gene. Escherichia coli BW25113 cells that synthesized Zn₃STe₂ QDs were used as environmentally friendly fluorescent bioprobes to specifically select and quantitatively detect Fe³⁺ in water with a low limit of detection (2.62 μM). The fluorescent cells were also photobleach resistant and had good fluorescence stability. This study expands on the synthesis method of telluride QDs and the application of fluorescent probes.

Magnetic biosensors for identification of SARS-CoV-2, Influenza, HIV, and Ebola viruses: a review

Infectious diseases such as novel coronavirus (SARS-CoV-2), Influenza, HIV, Ebola, etc kill many people around the world every year (SARS-CoV-2 in 2019, Ebola in 2013, HIV in 1980, Influenza in 1918). For example, SARS-CoV-2 has plagued higher than 317 000 000 people around the world from December 2019 to January 13, 2022. Some infectious diseases do not yet have not a proper vaccine, drug, therapeutic, and/or detection method, which makes rapid identification and definitive treatments the main challenges. Different device techniques have been used to detect infectious diseases. However, in recent years, magnetic materials have emerged as active sensors/biosensors for detecting viral, bacterial, and plasmids agents. In this review, the recent applications of magnetic materials in biosensors for infectious viruses detection have been discussed. Also, this work addresses the future trends and perspectives of magnetic biosensors.

Engineered Escherichia coli as a Controlled-Release Biocarrier for Electrochemical Immunoassay

Micro/nanocarriers hold great potential in bioanalysis for molecular recognition and signal amplification but are frequently hampered by harsh synthesis conditions and time-consuming labeling processes. Herein, we demonstrate that Escherichia coli (Ec) can be engineered as an efficient biocarrier for electrochemical immunoassay, which can load ultrahigh amounts of redox indicators and simultaneously be decorated with detection antibodies via a facile polydopamine (PDA)-mediated coating approach. Compared with conventional carrier materials, the entire preparation of the Ec biocarrier is simple, highly sustainable, and reproducible. Moreover, immune recognition and electrochemical transduction are performed independently, which eliminates the accumulation of biological interference on the electrode and simplifies electrode fabrication. Using human epidermal growth factor receptor 2 (HER2) as the model target, the proposed immunosensor exhibits excellent analytical performance with a low detection limit of 35 pg/mL. The successful design and deployment of Ec biocarrier may provide new guidance for developing biohybrids in biosensing applications.

Recent Development in Plasmonic Nanobiosensors for Viral DNA/RNA Biomarkers

Recently, due to the coronavirus pandemic, the need for early diagnosis of infectious diseases, including viruses, is emerging. Though early diagnosis is essential to prevent infection and progression to severe illness, there are few technologies that accurately measure low concentrations of biomarkers. Plasmonic nanomaterials are attracting materials that can effectively amplify various signals, including fluorescence, Raman, and other optical and electromagnetic output. In this review, we introduce recently developed plasmonic nanobiosensors for measuring viral DNA/RNA as potential biomarkers of viral diseases. In addition, we discuss the future perspective of plasmonic nanobiosensors for DNA/RNA detection. This review is expected to help the early diagnosis and pathological interpretation of viruses and other diseases.

AQDS Activates Extracellular Synergistic Biodetoxification of Copper and Selenite via Altering the Coordination Environment of Outer-Membrane Proteins

The biotransformation of heavy metals in the environment is usually affected by co-existing pollutants like selenium (Se), which may lower the ecotoxicity of heavy metals, but the underlying mechanisms remain unclear. Here, we shed light on the pathways of copper (Cu²⁺) and selenite (SeO₃^2-) synergistic biodetoxification by Shewanella oneidensis MR-1 and illustrate how such processes are affected by anthraquinone-2,6-disulfonate (AQDS), an analogue of humic substances. We observed the formation of copper selenide nanoparticles (Cu_2-xSe) from synergistic detoxification of Cu²⁺ and SeO₃^2- in the periplasm. Interestingly, adding AQDS triggered a fundamental transition from periplasmic to extracellular reaction, enabling 14.7-fold faster Cu²⁺ biodetoxification (via mediated electron transfer) and 11.4-fold faster SeO₃^2- detoxification (via direct electron transfer). This is mainly attributed to the slightly raised redox potential of the heme center of AQDS-coordinated outer-membrane proteins that accelerates electron efflux from the cells. Our work offers a fundamental understanding of the synergistic detoxification of heavy metals and Se in a complicated environmental matrix and unveils an unexpected role of AQDS beyond electron mediation, which may guide the development of more efficient environmental remediation and resource recovery biotechnologies.

High-Performance and Broadband Flexible Photodetectors Employing Multicomponent Alloyed 1D CdSxSe1-x Micro-Nanostructures

Low-cost multicomponent alloyed one-dimensional (1D) semiconductors exhibit broadband absorption from the ultraviolet to the near-infrared regime, which has attracted a great deal of interest in high-performance flexible optoelectronic devices. Here, we report the facile one-step fabrication of high-performance broadband rigid and flexible photodevices based on multicomponent alloyed 1D cadmium-sulfur-selenide (CdS_xSe_1-x) micro-nanostructures obtained via a vapor transport route. Photoresponse measurements have demonstrated their superior spectral photoresponsivity (5.8 × 10⁴ A/W), several orders of magnitude higher than the pristine CdSe nanobelt photodevice, high specific detectivity (2 × 10¹⁵ Jones), photogain (1.2 × 10⁵), external quantum efficiency (EQE, 1.4 × 10⁷%), rapid response speed (13 ms), and excellent long-term environmental stability. The multicomponent alloyed CdS_xSe_1-x nanobelt photodevice demonstrated about three times higher photocurrent as well as can operate under multiple color illuminations (200-800 nm) and at a high applied bias of 10 V with the photoresponsivity and EQE being boosted to 4.34 × 10⁵ A/W and 8.96 × 10⁷%, respectively. Furthermore, multicomponent alloyed CdS_xSe_1-x nanobelt flexible photodevices show excellent mechanical and flexural photostabilities with identical photoresponse as rigid nanodevices. The improvement mechanism found in the present research can be exploited to lead to the design of high-performance flexible photodevices comprising other multicomponent nanomaterials.

Dual-Modal Immunochromatographic Test for Sensitive Detection of Zearalenone in Food Samples Based On Biosynthetic Staphylococcus aureus-Mediated Polymer Dot Nanocomposites

The rapid detection of toxins is of great significance to food security and human health. In this work, a dual-modality immunochromatographic test (DICT) mediated by Staphylococcus aureus (SA)-biosynthesized polymer dots (SABPDs) was constructed for sensitive monitoring of zearalenone (ZEN) in agro products. The SABPDs as potent microorganism nanoscaffolds with excellent solubility, brightness, and stability were ingeniously fabricated employing hydroquinone and SA as precursors in the Schiff base reaction and a self-assembly technique. Thanks to the fact that they not only preserved an intact microsphere for loading Fc regions of monoclonal antibodies (mAbs) and the affinity of their labeled mAbs to antigen but also generated superb colorimetric-fluorescent dual signals, the versatile SABPDs manifested unique possibilities as the new carriers for dual-readout ICT with remarkable enhancement in sensitivity in ZEN screening (limit of detection = 0.036 ng/mL, which was 31-fold lower than that of traditional gold nanoparticle-based ICT). Ultimately, the proposed immunosensor performed well in millet and corn samples with satisfactory recoveries, demonstrating its potential for point-of-care testing. This work offers a bio-friendly strategy for biosynthesizing cell-based PD vehicles with bimodal signals for food safety analysis.

Ultrasmall MnSe Nanoparticles as T1-MRI Contrast Agents for In Vivo Tumor Imaging

Magnetic resonance imaging (MRI) has excellent potential in the clinical monitoring of tumors because it can provide high-resolution soft tissue imaging. However, commercial contrast agents (CAs) used in MRI still have some problems such as potential toxicity to the human body, low relaxivity, and a short MRI acquisition window. In this study, ultrasmall MnSe nanoparticles are synthesized by living Staphylococcus aureus cells. The as-prepared MnSe nanoparticles are monodispersed with a uniform particle size (3.50 ± 0.52 nm). Due to the ultrasmall particle size and good water solubility, the MnSe nanoparticles exhibit in vitro high longitudinal relaxivity properties (14.12 ± 1.85 mM-1·s-1). The CCK-8 colorimetric assay, histological analysis, and body weight results show that the MnSe nanoparticles do not have appreciable toxicity on cells and organisms. Besides, the MnSe nanoparticles as T1-MRI CAs offer a long MRI acquisition window to tumor imaging (∼7 h). This work provides a promising T1-MRI CA for clinical tumor imaging and a good reference for the application of functional MnSe nanoparticles in the biomedicine field.

Organelle targeting using a fluorescent probe that selectively penetrates the zona pellucida

The characteristics of oocytes, which are female germ cells, have not been studied using optical materials. The structural layers (zona pellucida, ZP) around oocytes make it difficult to deliver drugs aimed at treating infertility. Here, we investigated whether the fluorescent probes sulforhodamine, fluorescein 5(6)-isothiocyanate, tetramethylrhodamine isothiocyanate, cyanine 3 carboxylic acid, and cyanine 5 carboxylic acid penetrate oocytes. By targeting the ZP layer of the oocyte, the characteristics of the model drug, a fluorescent probe, were analyzed, and the position of the probe in the oocyte was confirmed for differences in the characteristics. Penetration of the ZP and delivery into the cytoplasm differed between the fluorescent probes. This was due to their different physiochemical properties, including hydrophobicity (contact angle and surface tension), surfactant activity, and electrical charge. Among the fluorescent probes delivered to cytoplasm, unlike TRITC, Cy3 and Cy5 perturbed oocyte development. These results suggest that in oocytes with high physical barriers (cell membrane, zona pellucida), the delivery efficiency can be estimated by considering the properties (molecular weight and structure, solubility and functional structure, etc.) of the drug. In addition, it suggests that an encapsulated or bound carrier of a drug with properties similar to that of a fluorescent probe can be efficiently delivered into oocytes.

Rapid Naked-Eye Detection of a Liver Disease Biomarker by Discovering Its Monoclonal Antibody to Functionalize Engineered Red-Colored Bacteria Probes

Glycocholic acid (GCA) is a biomarker for liver diseases, but few facile naked-eye detection methods have been reported to detect it till now. To tackle this challenge, we first prepared a novel monoclonal mouse antibody (mAb) of GCA by a hybridoma technique. The anti-GCA mAb exhibited high specificity, making its cross-reactivity with seven structurally and functionally related GCA analogs negligible. Using this anti-GCA mAb and an engineered red-colored bacterial strain (Staphylococcus aureus, S. aureus), we developed a simple naked-eye visualized method for GCA detection. Toward this goal, S. aureus bacteria were turned red by 5-cyano-2,3-ditolyl tetrazolium chloride treatment and heat treated to an unculturable state, rendering the bacteria as an optical detection probe powerful in in vitro diagnostics. Through the natural binding ability of protein A on the surface of S. aureus and the Fc fragment of a mouse antibody, the anti-GCA antibody was simply conjugated onto S. aureus. Then, the engineered S. aureus served as a red-colored bioprobe for detecting GCA through a coagglutination test. In the presence of GCA, the bioprobes aggregated into dense red-colored eye-visible clusters, enabling the sensitive detection of GCA with a concentration of 0.05-0.10 μg/mL. This naked-eye visualization method only takes a few minutes to detect GCA and avoids the use of expensive equipment. It represents a rapid, convenient, and simple method for detecting GCA to diagnose liver diseases.

Current advances in bio-fabricated quantum dots emphasising the study of mechanisms to diversify their catalytic and biomedical applications

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

Artificial-regulated synthesis of nanocrystals in live cells

Live cells, as reservoirs of biochemical reactions, can serve as amazing integrated chemical plants where precursor formation, nucleation and growth of nanocrystals, and functional assembly can be carried out accurately following an artificial program. It is crucial but challenging to deliberately direct intracellular pathways to synthesize desired nanocrystals that cannot be produced naturally in cells, because the relevant reactions exist in different spatiotemporal dimensions and will never encounter spontaneously. This article summarizes progress in the introduction of inorganic functional nanocrystals into live cells via the ‘artificial-regulated space–time-coupled live-cell synthesis’ strategy. We also describe ingenious bio-applications of the nanocrystal–cell systems, and quasi-biosynthesis strategies expanded from live-cell synthesis. Artificial-regulated live-cell synthesis—which involves the interdisciplinary application of biology, chemistry, nanoscience and medicine—will enable researchers to better exploit the unanticipated potentialities of live cells and open up new directions in synthetic biology.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

Multifunctional bacteria-derived tags for advancing immunoassay analytical performance with dual-channel switching and antibodies bioactivity sustaining

Constructing multifunctional immunochromatographic assays (ICA) carriers with multiple signals and retaining bioactivity of monoclonal antibodies (mAbs) are conducive to the sensitive and accurate point-of-care testing (POCT). To fulfill this pressing need, a microorganism-based microsphere mediated dual-modal ICA (DICA) was developed for sensitive and reliable detection of zearalenone (ZEN). As the key to the biosensor, a superb biotag with an intact coccus morphology was designed based on Staphylococcus aureus biosynthesized quantum dots incorporating Ru(bpy)₃²⁺ (SAQDsRu), in which SA offered a specific recognition capacity for Fc region of mAbs, QDs endowed a naked-eye discernible colorimetric signal on the SA, and robust fluorescence signal that remedied for the insufficient brightness of QDs was derived from Ru(bpy)₃²⁺. The characterization of SAQDsRu-labeled mAb (SAQDsRu-mAb) probe demonstrated strong luminescence, excellent stability and high affinity with ZEN (affinity constant was approximately 1.723 × 10⁹ M^-1), which can significantly improve the detection sensitivity. Impressively, a portable sensing system was developed by the integration of SAQDsRu-DICA with a smartphone-based readout. After optimization, this DICA indicated a limit of detection reaching down to 0.008 ng/mL (colorimetric mode) and 0.0058 ng/mL (fluorescent mode), which were much lower than that of conventional gold nanoparticles-based ICA (0.1029 ng/mL), possessing favorable specificity and repeatability (relative standard deviation (RSD) < 10%). Moreover, the feasibility of the immunoassay was further assessed by measuring ZEN in real samples with satisfactory recoveries, and the results are good consistent with liquid chromatography tandem mass spectrometry (LC-MS/MS).

Roles of cation efflux pump in biomineralization of cadmium into quantum dots in Escherichia coli

Cadmium (Cd) is a typical and widely present toxic heavy metals in environments. Biomineralization of Cd ions could alleviate the toxicity and produce valuable products in certain waste streams containing selenite. However, the impact of the intrinsic Cd(II) efflux system on the biotransformation process remains unrevealed. In this work, the significance of the efflux system on Cd biomineralization was evaluated by constructing engineered Escherichia coli strains, including ΔzntA with suppressed Cd(II) efflux system and pYYDT-zntA with strengthened Cd(II) efflux system. Compared to the wild type (WT), 20% more Cd ions were accumulated in ΔzntA and 17% less were observed in pYYDT-zntA in the presence of selenite as determined by inductively coupled plasma atomic emission spectrometer. Through combination with X-ray absorption fine structure analysis, it was discovered that 50% higher production of CdS_xSe_1-x quantum dots (QDs) was achieved in the ΔzntA cells than that in the WT cells. Moreover, the ΔzntA cells exhibited the same viability as the WT cells and the pYYDT-zntA cells because accumulated Cd ions were transformed into biocompatible QDs. In addition, the biosynthesized QDs had a uniform particle size (3.82 ± 0.53 nm) and a long fluorescence lifetime (45.6 ns), which could potentially be utilized for bio-imaging. These results not only elucidate the significance of Cd(II) efflux system in the biotransformation of Cd ions and selenite, but also provide a promising way to recover Cd and Se as valuable products in certain waste streams.

Tumor-targeting inorganic nanomaterials synthesized by living cells

Inorganic nanomaterials (NMs) have shown potential application in tumor-targeting theranostics, owing to their unique physicochemical properties. Some living cells in nature can absorb surrounding ions in the environment and then convert them into nanomaterials after a series of intracellular/extracellular biochemical reactions. Inspired by that, a variety of living cells have been used as biofactories to produce metallic/metallic alloy NMs, metalloid NMs, oxide NMs and chalcogenide NMs, which are usually automatically capped with biomolecules originating from the living cells, benefitting their tumor-targeting applications. In this review, we summarize the biosynthesis of inorganic nanomaterials in different types of living cells including bacteria, fungi, plant cells and animal cells, accompanied by their application in tumor-targeting theranostics. The mechanisms involving inorganic-ion bioreduction and detoxification as well as biomineralization are emphasized. Based on the mechanisms, we describe the size and morphology control of the products via the modulation of precursor ion concentration, pH, temperature, and incubation time, as well as cell metabolism by a genetic engineering strategy. The strengths and weaknesses of these biosynthetic processes are compared in terms of the controllability, scalability and cooperativity during applications. Future research in this area will add to the diversity of available inorganic nanomaterials as well as their quality and biosafety.

Diverse Dyes-Embedded Staphylococcus aureus as Potential Biocarriers for Enhancing Sensitivity in Biosensing

Nanomaterials-based immunochromatographic assays (ICAs) have gained great commercial success in real-life point-of-care testing (POCT). Exploring novel carriers of ICAs with improved signaling and sustained activity favors the development of sensitive POCT. Herein a potent signal biotag, colored Staphylococcus aureus (SA), was created for ICA carriers through a mild self-assembly strategy, providing high luminance and abundant specific binding sites for immobilization of monoclonal antibodies (mAbs). The biocompatible SA-dyes (SADs) retained both an intact surface structure for mAbs labeling (Fc portion) and the superior bioactivity of immobilized mAbs (affinity constant was about 10⁹ M^-1), thus waiving the intrinsic limitations of traditional nanomaterials and endowing high sensitivity. Proof-of-concept was demonstrated by employing Congo red- or/and fluorescein isothiocyanate-embedded SA (SACR, SAFITC, and SACR-SAFITC) as ICA carriers to detect zearalenone (ZEN) through colorimetric or/and fluorimetric signals. Furthermore, the ICAs satisfied the clinical requirement perfectly, including limit of detection (0.013 ng/mL, which was at least an 85-fold improvement over that of traditional gold nanoparticles-based ICA), linearity (R² > 0.98), reproducibility (RSD < 8%), selectivity, and stability. Importantly, the proposed biosensors could be well-applied in four real samples for ZEN monitoring with satisfactory recoveries, correlating well with the results from liquid chromatography-tandem mass spectrometry (LC-MS). This work also proved a universal design for tailoring coloration bands for SAD-ICA detection of multiple analytes.

Optical Biosensors for Virus Detection: Prospects for SARS-CoV-2/COVID-19

The recent pandemic of the novel coronavirus disease 2019 (COVID-19) has caused huge worldwide disruption due to the lack of available testing locations and equipment. The use of optical techniques for viral detection has flourished in the past 15 years, providing more reliable, inexpensive, and accurate detection methods. In the current minireview, optical phenomena including fluorescence, surface plasmons, surface-enhanced Raman scattering (SERS), and colorimetry are discussed in the context of detecting virus pathogens. The sensitivity of a viral detection method can be dramatically improved by using materials that exhibit surface plasmons or SERS, but often this requires advanced instrumentation for detection. Although fluorescence and colorimetry lack high sensitivity, they show promise as point-of-care diagnostics because of their relatively less complicated instrumentation, ease of use, lower costs, and the fact that they do not require nucleic acid amplification. The advantages and disadvantages of each optical detection method are presented, and prospects for applying optical biosensors in COVID-19 detection are discussed.

Biosynthesized Quantum Dots as Improved Biocompatible Tools for Biomedical Applications

Quantum Dots (QDs), whose diameters are often limited to 10 nm, have been of interest to researchers for their unique optical characteristics, which are attributed to quantum confinement. Following their early application in the electrical industry as light-emitting diode materials, semiconductor nanocrystals have continued to show great potential in clinical diagnosis and biomedical applications. The conventional physical and chemical pathways for QD syntheses typically require harsh conditions and hazardous reagents, and these products encounter non-hydrophilic problems due to organic capping ligands when they enter the physiological environment. The natural reducing abilities of living organisms, especially microbes, are then exploited to prepare QDs from available metal precursors. Low-cost and eco-friendly biosynthesis approaches have the potential for further biomedical applications which benefit from the good biocompatibility of protein-coated QDs. The surface biomass offers many binding sites to modify substances or target ligands, therefore achieving multiple functions through simple and efficient operations. Biosynthetic QDs could function as bioimaging and biolabeling agents because of their luminescence properties similar to those of chemical QDs. In addition, extensive research has been carried out on the antibacterial activity, metal ion detection and bioremediation. As a result, this review details the advanced progress of biomedical applications of biosynthesized QDs and illustrates these principles as clearly as possible.

Point of Care Diagnostics in Resource-Limited Settings: A Review of the Present and Future of PoC in Its Most Needed Environment

Point of care (PoC) diagnostics are at the focus of government initiatives, NGOs and fundamental research alike. In high-income countries, the hope is to streamline the diagnostic procedure, minimize costs and make healthcare processes more efficient and faster, which, in some cases, can be more a matter of convenience than necessity. However, in resource-limited settings such as low-income countries, PoC-diagnostics might be the only viable route, when the next laboratory is hours away. Therefore, it is especially important to focus research into novel diagnostics for these countries in order to alleviate suffering due to infectious disease. In this review, the current research describing the use of PoC diagnostics in resource-limited settings and the potential bottlenecks along the value chain that prevent their widespread application is summarized. To this end, we will look at literature that investigates different parts of the value chain, such as fundamental research and market economics, as well as actual use at healthcare providers. We aim to create an integrated picture of potential PoC barriers, from the first start of research at universities to patient treatment in the field. Results from the literature will be discussed with the aim to bring all important steps and aspects together in order to illustrate how effectively PoC is being used in low-income countries. In addition, we discuss what is needed to improve the situation further, in order to use this technology to its fullest advantage and avoid “leaks in the pipeline”, when a promising device fails to take the next step of the valorization pathway and is abandoned.

Developments in the study and applications of bacterial transformations of selenium species

Microbial bio-transformations of the essential trace element selenium are now recognized to occur among a wide variety of microorganisms. These transformations are used to convert this element into its assimilated form of selenocysteine, which is at the active center of a number of key enzymes, and to produce selenium nanoparticles, quantum dots, metal selenides, and methylated selenium species that are indispensable for biotechnological and bioremediation applications. The focus of this review is to present the state-of-the-art of all aspects of the investigations into the bacterial transformations of selenium species, and to consider the characterization and biotechnological uses of these transformations and their products.

Ultrasensitive Visualization of Virus via Explosive Catalysis of an Enzyme Muster Triggering Gold Nano-aggregate Disassembly

Sensitive and accurate diagnosis of viral infection is important for human health and social safety. Herein, by means of explosive catalysis from an enzyme muster, a powerful naked-eye readout platform has been successfully constructed for ultrasensitive immunoassay of viral entities. Liposomes were used to encapsulate multiple enzymes into an active unit. In addition, its triggered rupture could boost the disassembly of gold nano-aggregates that were cross-linked by peptides with opposite charges. As a result, plasmonically colorimetric signals were rapidly generated for naked-eye observation. Further harnessing the immunocapture, enterovirus 71 (EV71), a class of highly infective virus, was sensitively assayed with a detection limit down to 16 copies/μL. It is superior to the single enzyme-anchored immunoassay system. Most importantly, the colorimetric assay was demonstrated with 100% clinical accuracy, displaying strong anti-interference capability. It is expectable that this sensitive, accurate, and convenient strategy could provide a prospective alternative for viral infection analysis, especially in resource-constrained settings.

Staphylococcus aureus strains exposed to copper indium sulfide quantum dots exhibit increased tolerance to penicillin G, tetracycline and ciprofloxacin

Copper indium sulfide, CuInS₂ (CIS), semiconductor nanocrystals have the qualities of low toxicity, high absorption coefficient and near-infrared luminescence, and thus have attracted increasing attention due to their wide prospective applications in various fields.

Biosynthesized Quantum Dot for Facile and Ultrasensitive Electrochemical and Electrochemiluminescence Immunoassay

Nanomaterials are commonly utilized for amplified immunoassay of biomarkers. However, traditional nanomaterial-based immunoassay usually requires a time-consuming and labor-intensive nanoparticle modification and conjugation process, which impedes their practical applications. Here, a new immunoassay method based on biosynthesized nanomaterials is developed with versatile functions for facile and ultrasensitive detection of cancer biomarker. In this method, the utilized biosynthesized quantum dots (BQDs) allow convenient antibody conjugation and electrode modification, and demonstrate excellent electrochemical and electrochemiluminescent responses. The differential pulse voltammetric, faradaic impedance spectroscopy, and electrochemiluminescent measurements with the BQD-modified electrode show detection limits at picomolar levels as well as good specificity toward human prostate-specific antigen detection. The inherent recognization capability as well as the inherent electrochemical and electrochemiluminescence features thus enable BQDs as good candidates for facile immunosensors with high sensitivity. Such a biosynthesized nanomaterial-based approach opens up the possibility of using innovative designs for nanoparticle-based assays, and developing reliable and practical methods for early disease diagnosis.

Dual-mode detection of avian influenza virions (H9N2) by ICP-MS and fluorescence after quantum dot labeling with immuno-rolling circle amplification

Avian influenza virus (AIVs), hosted in poultry, are the pathogens of many poultry diseases and human infections, which bring huge losses to the poultry breeding industry and huge panic to society. Therefore, it is of great significance to establish accurate and sensitive detection methods for AIVs. In this work, a dual-mode detection method based on immuno-rolling circle amplification (immuno-RCA) and quantum dots (QDs) labeling for inductively coupled plasma mass spectrometry (ICP-MS) and fluorescence detection of H9N2 AIV was developed. The dual-mode detection of the QDs by ICP-MS and fluorescence is used to achieve mutual verification within the analysis results, thus improving the accuracy of the method. With the immuno-RCA, the sensitivity of the method was increased by two orders of magnitude. The limit of detection of the proposed method is 17 ng L^-1 and 61 ng L^-1, and the linear range of the proposed method is 0.05-5 ng mL^-1 and 0.1-5 ng mL^-1 with ICP-MS and fluorescence detection, respectively. The relative standard deviation (n = 7) is 4.9% with ICP-MS detection and 3.1% with fluorescence detection. Furthermore, the proposed method was applied to the analysis of chicken serum samples, no significant different was found for two modes detection and the recoveries of the spiking experiments are acceptable, indicating that the method has good practical potential for real sample analysis.

A novel cadmium-containing wastewater treatment method: Bio-immobilization by microalgae cell and their mechanism

Heavy metal cadmium (Cd) has drawn tremendous comcern due to its rigorous environmental and health hazards. Herein, we have presented an efficient and economical strategy for the removal and recycling of hazardous Cd ions using microalgae cells as the bioreactors. Remarkably, the green bio-platform for the bioproduction of CdSe nanoparticles (NPs) was developed depending on their orderly regulated and sustainable cellular environment. The biofabricated CdSe NPs manifested favorable photoluminescence properties, and presented well monodispersed spherical morphology and certain crystallinity structure with mean size of smaller than 7 nm. Especially, the fluorescence "turn off" sensing system based on the CdSe NPs was established to detect Hg²⁺. The nanosensor enables the quantitative analyses of Hg²⁺ with a linear range of 0-2.0 μM and a detection limit of 0.021 μM. Furthermore, it was preliminarily speculated that the reducing biomolecules in the algae cells could be involved in the formation of CdSe NPs. This work not only provides new insights into the removal and recycling of hazardous Cd ions, but also brings a promising route for biosynthesis of CdSe NPs.

Substrate Metabolism-Driven Assembly of High-Quality CdS xSe1- x Quantum Dots in Escherichia coli: Molecular Mechanisms and Bioimaging Application

Biosynthesis offers opportunities for cost-effective and sustainable production of semiconductor quantum dots (QDs), but is currently restricted by poor controllability on the synthesis process, resulting from limited knowledge on the assembly mechanisms and the lack of effective control strategies. In this work, we provide molecular-level insights into the formation mechanism of biogenic QDs (Bio-QDs) and its connection with the cellular substrate metabolism in Escherichia coli. Strengthening the substrate metabolism for producing more reducing power was found to stimulate the production of several reduced thiol-containing proteins (including glutaredoxin and thioredoxin) that play key roles in Bio-QDs assembly. This effectively diverted the transformation route of the selenium (Se) and cadmium (Cd) metabolic from Cd₃(PO₄)₂ formation to CdS _xSe_{1- x} QDs assembly, yielding fine-sized (2.0 ± 0.4 nm), high-quality Bio-QDs with quantum yield (5.2%) and fluorescence lifetime (99.19 ns) far exceeding the existing counterparts. The underlying mechanisms of Bio-QDs crystallization and development were elucidated by density functional theory calculations and molecular dynamics simulation. The resulting Bio-QDs were successfully used for bioimaging of cancer cells and tumor tissue of mice without extra modification. Our work provides fundamental knowledge on the Bio-QDs assembly mechanisms and proposes an effective, facile regulation strategy, which may inspire advances in controlled synthesis and practical applications of Bio-QDs as well as other bionanomaterials.

AIE-based theranostic systems for detection and killing of pathogens

Pathogenic bacteria, fungi and viruses pose serious threats to the human health under appropriate conditions. There are many rapid and sensitive approaches have been developed for identification and quantification of specific pathogens, but many challenges still exist. Culture/colony counting and polymerase chain reaction are the classical methods used for pathogen detection, but their operations are time-consuming and laborious. On the other hand, the emergence and rapid spread of multidrug-resistant pathogens is another global threat. It is thus of utmost urgency to develop new therapeutic agents or strategies. Luminogens with aggregation-induced emission (AIEgens) and their derived supramolecular systems with unique optical properties have been developed as fluorescent probes for turn-on sensing of pathogens with high sensitivity and specificity. In addition, AIE-based supramolecular nanostructures exhibit excellent photodynamic inactivation (PDI) activity in aggregate, offering great potential for not only light-up diagnosis of pathogen, but also image-guided PDI therapy for pathogenic infection.

Introduction into nanotechnology and microbiology

The current chapter summaries the world of Microbiology and boom of Nanotechnology and how both the exciting fields come together to help men kind with various new applications in water, food, medical biology and immunology. Furthermore synthesis of nano materials utilising the potential of microorganisms also opens a newer avenue for 'green' synthesis.

AIE Featured Inorganic-Organic Core@Shell Nanoparticles for High-Efficiency siRNA Delivery and Real-Time Monitoring

RNA interference (RNAi) is demonstrated as one of the most powerful technologies for sequence-specific suppression of genes in disease therapeutics. Exploration of novel vehicles for small interfering RNA (siRNA) delivery with high efficiency, low cytotoxicity, and self-monitoring functionality is persistently pursued. Herein, by taking advantage of aggregation-induced emission luminogen (AIEgen), we developed a novel class of Ag@AIE core@shell nanocarriers with regulable and uniform morphology. It presented excellent efficiencies in siRNA delivery, target gene knockdown, and cancer cell inhibition in vitro. What's more, an anticancer efficacy up to 75% was achieved in small animal experiments without obvious toxicity. Attributing to the unique AIE properties, real-time intracellular tracking of siRNA delivery and long-term tumor tissue imaging were successfully realized. Compared to the commercial transfection reagents, significant improvements were obtained in biocompatibility, delivery efficiency, and reproducibility, representing a promising future of this nanocarrier in RNAi-related cancer therapeutics.

The essentialness of glutathione reductase GorA for biosynthesis of Se(0)-nanoparticles and GSH for CdSe quantum dot formation in Pseudomonas stutzeri TS44

Pseudomonas stutzeri TS44 was able to aerobically reduce Se(IV) into SeNPs and transform Se(IV)/Cd(II) mixture into CdSe-QDs. The SeNPs and CdSe-QDs were systematically characterized by surface feature analyses, and the molecular mechanisms of SeNPs and CdSe-QD formation in P. stutzeri TS44 were characterized in detail. In vivo, under 2.5 mmol/L Se(IV) exposure, GorA was essential for catalyzing of Se(IV) reduction rate decreased by 67% when the glutathione reductase gene gorA was disrupted, but it was not decreased in the glutathione synthesis rate-limiting gene gshA mutated strain compared to the wild type. The complemented strains restored the phenotypes. While under low amount of Se(IV) (0.5 mmol/L), GSH played an important role for Se(IV) reduction. In vitro, GorA catalyzed Se(IV) reduction with NADPH as the electron donor (Vmax of 3.947 ± 0.1061 μmol/min/mg protein under pH 7.0 and 28℃). In addition, CdSe-QDs were successfully synthesized by a one-step method in which Se(IV) and Cd(II) were added to bacterial culture simultaneously. GSH rather than GorA is necessary for CdSe-QD formation in vivo and in vitro. In conclusion, the results provide new findings showing that GorA functions as a selenite reductase under high amount Se(IV) and GSH is essential for bacterial CdSe-QD synthesis.

Antibiotic-Derived Lipid Nanoparticles to Treat Intracellular Staphylococcus aureus

Intracellular survival of pathogenic bacteria leads to high chances of bacterial persistence and relapse in the bacteria-infected host. However, many antibiotics fail to clear the intracellular bacteria due to their low internalization by cells. In order to increase delivery of antibiotics in cells and eliminate intracellular bacteria, we developed antibiotic-derived lipid nanoparticles. First, we synthesized antibiotic-derived lipid conjugates using two widely used antibiotics including penicillin G (PenG) and levofloxacin (Levo). Then, we formulated them into antibiotic-derived lipid nanoparticles and evaluated their antibacterial effects. We found that penicillin G derived phospholipid nanoparticles (PenG-PL NPs) were able to enhance cellular uptake of penicillin G as compared with free penicillin G and eliminate up to 99.9998% of ~10^8.5 intracellular methicillin sensitive Staphylococcus aureus (S. aureus) in infected A549 cells, a lung epithelial cell line. The PenG-PL NPs showed the potential for inhibiting intracellular S. aureus and are promising to be further studied for in vivo antibacterial applications.

A novel colorimetric sensing platform for the detection ofS. aureuswith high sensitivity and specificity

In this study, a novel colorimetric sensing platform was developed for the detection of S. aureus using dog immunoglobulin G (IgG) as the capture antibody and chicken anti-protein A immunoglobulin Y labeled with horseradish peroxidase (HRP-IgY) as the detection antibody. Dog IgG labeled with magnetic beads was used to capture S. aureus through the interaction between the Fc region of dog IgG and Staphylococcal protein A (SPA). HRP-IgY was introduced to recognize the residual SPA on the surface of S. aureus and to create a sandwich format, after which a soluble 3,3′,5,5′-tetramethylbenzidine (TMB) substrate was added. A stop solution was utilized to cease the enzymatic chromogenic reaction, and then optical density was read at 450 nm. Under optimal conditions, the proposed method displayed a low detection limit of 1.0 × 10³ CFU mL⁻¹ and a wide linear range of 3.1 × 10³ to 2.0 × 10⁵ CFU mL⁻¹. This detection method exhibited high specificity against other foodborne bacteria. The recovery rates ranged from 95.2% to 129.2%. To our knowledge, this is the first report to employ dog IgG and chicken IgY as an antibody pair to detect S. aureus. This technique exhibits high application potential for S. aureus monitoring in various kinds of samples.

Utilization of dog IgG and chicken anti-protein A IgY as an antibody pair for sensitive and selective detection of S. aureus.