Aggregation-free optical and colorimetric detection of Hg(II) with M13 bacteriophage-templated Au nanowires

The controllable synthesis of multi-color carbon quantum dots modified by polythiophene and their application in fluorescence detection of Au3+ and Hg2

Herein, hydrothermal method was used to prepare a series of multi-color polythiophene modified carbon quantum dots. Under UV excitation, fluorescence their maximum emission wavelengths appear at 612 nm, 570 nm, and 540 nm respectively. The prepared CD-BTH and CD-BN can have specific detection of Au3+ and Hg2+ through fluorescence quenching effect. The detection limits for Au3+ are 3 nM and 5.4 nM respectively, and for Hg2+ are 23 nM and 90 nM respectively. CD-KN detects Au3+ specifically through fluorescence resonance, with a detection limit of 33 nM. Under the interference of other metal ions, three types of polythiophene modified quantum carbon dots exhibit excellent selectivity for the responsive ions. Meanwhile, this article also elucidates the law that as the electron withdrawing ability of the side chains of polythiophene derivatives increasing, the fluorescence emission peaks of the prepared polythiophene modified carbon dots shifts red and the fluorescence quantum yield is higher.

Genetically engineered bacteriophages as novel nanomaterials: applications beyond antimicrobial agents

Bacteriophages, also known as phages, are viruses that replicate in bacteria and archaea. Phages were initially discovered as antimicrobial agents, and they have been used as therapeutic agents for bacterial infection in a process known as "phage therapy." Recently, phages have been investigated as functional nanomaterials in a variety of areas, as they can function not only as therapeutic agents but also as biosensors and tissue regenerative materials. Phages are nontoxic to humans, and they possess self-assembled nanostructures and functional properties. Additionally, phages can be easily genetically modified to display specific peptides or to screen for functional peptides via phage display. Here, we demonstrated the application of phage nanomaterials in the context of tissue engineering, sensing, and probing.

A Fluorescence Biosensor Based on Carbon Quantum Dots Prepared from Pomegranate Peel and T-Hg2+-T Mismatch for Hg2+ Detection

Mercury ions (Hg2+) can cause damage to human health, and thus, the study of the detection of Hg2+ is extraordinarily important in daily life. This work reported a fluorescence biosensor for the detection of Hg2+. The key point of this strategy was that the fluorescence of carbon quantum dots made from pomegranate peel (P-CQDs) was quenched by hemin, and restored after G-quadruplex binding with hemin. The presence of Hg2+ caused thymine (T)-rich DNA fragments to form T-Hg2+-T mismatches, and this change allowed the release of G-quadruplex. G-quadruplex could change the fluorescence of hemin/P-CQDs. P-CQDs exhibited excellent properties through characterization analysis, such as transmission electron microscope, X-ray photoelectron spectroscopy and Fourier transform infrared. This proposed fluorescence detection strategy established the linear ranges of Hg2+ from 1 nM to 50 nM. In conclusion, this simple biosensor had the advantages of strong sensitivity, high selectivity, and low cost for Hg2+ detection in environmental water samples.

M13 Bacteriophage-Assisted Recognition and Signal Spatiotemporal Separation Enabling Ultrasensitive Light Scattering Immunoassay

The demand for the ultrasensitive and rapid quantitative analysis of trace target analytes has become increasingly urgent. However, the sensitivity of traditional immunoassay-based detection methods is limited due to the contradiction between molecular recognition and signal amplification caused by the size effect of nanoprobes. To address this dilemma, we describe versatile M13 phage-assisted immunorecognition and signal transduction spatiotemporal separation that enable ultrasensitive light-scattering immunoassay systems for the quantitative detection of low-abundance target analytes. The newly developed immunoassay strategy combines the M13 phage-assisted light scattering signal fluctuations of gold nanoparticles (AuNPs) with gold in situ growth (GISG) technology. Given the synergy of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation, the practical detection capability of this strategy can achieve the ultrasensitive and rapid quantification of ochratoxin A and alpha-fetoprotein in real samples at the subfemtomolar level within 50 min, displaying about 4 orders of magnitude enhancement in sensitivity compared with traditional phage-based ELISA. To further improve the sensitivity of our immunoassay, the biotin-streptavidin amplification scheme is implemented to detect severe acute respiratory syndrome coronavirus 2 spike protein down to the attomolar range. Overall, this study offers a direction for ultrasensitive quantitative detection of target analytes by the synergistic combination of M13 phage-mediated leverage effect and GISG-amplified light scattering signal modulation.

Advance on Engineering of Bacteriophages by Synthetic Biology

Since bacteriophages (phages) were firstly reported at the beginning of the 20th century, the study on them experiences booming-fading-emerging with discovery and overuse of antibiotics. Although they are the hotspots for therapy of antibiotic-resistant strains nowadays, natural phage applications encounter some challenges such as limited host range and bacterial resistance to phages. Synthetic biology, one of the most dramatic directions in the recent 20-years study of microbiology, has generated numerous methods and tools and has contributed a lot to understanding phage evolution, engineering modification, and controlling phage-bacteria interactions. In order to better modify and apply phages by using synthetic biology techniques in the future, in this review, we comprehensively introduce various strategies on engineering or modification of phage genome and rebooting of recombinant phages, summarize the recent researches and potential directions of phage synthetic biology, and outline the current application of engineered phages in practice.

Facile synthesis of dual-ligand terbium-organic gels as ratiometric fluorescence probes for efficient mercury detection

Mercury (Hg) pollution can negatively impact ecosystems, and there is a need for simple Hg²⁺ monitoring platforms. Here, a dual-ligand fluorescence probe based on terbium-organic gels (Tb-L_0.2P_0.8 MOGs) was constructed for efficient Hg²⁺ detection. Tb-L_0.2P_0.8 MOGs were developed through a facile room-temperature gelation method, showing two emission peaks derived from luminol and Tb³⁺ at 424 nm and 544 nm, respectively. The aggregation-induced emission (AIE) effect between luminol and Tb³⁺ led to luminol with blue fluorescence. However, Hg²⁺ could dramatically quench the fluorescence signal of luminol at 424 nm because of the intense coordination interaction of Hg²⁺ with luminol and photo-induced electron transfer (PET). The Phen ligand could sensitize the luminescence of Tb³⁺ and offer a reference fluorescence, thus resulting in a unique ratiometric fluorescence response toward Hg²⁺. This novel nanoprobe had excellent linearity with Hg²⁺ concentrations range of 0.1-30 μM; the detection limit was 3.6 nM. The analysis of real samples showed the potential application of MOGs for measuring Hg²⁺ in porphyra and tap water. Mixed ligands were introduced for high-efficiency strategies to improve the analytical performance by regulating the emission behavior of MOGs.

Fast and efficient "on-off-on" fluorescent sensor from N-doped carbon dots for detection of mercury and iodine ions in environmental water

A kind of nitrogen doped carbon dots (N-CDs) was facilely fabricated from polyethyleneimine and anhydrous citric acid, and which was adopted to develop a neoteric "on-off" and "off-on" fluorescent sensor for rapidly and efficiently sensing Hg²⁺ and I^-. The fluorescence of N-CDs was notably quenched (off) in the existence of Hg²⁺ derived from strong interaction and the electron transfer between N-CDs and Hg²⁺, while the quenched fluorescence of the N-CDs and Hg²⁺ system was strikingly regained by addition of I^- (on) resulted from the separation of N-CDs and Hg²⁺ due to the higher binding preference between Hg²⁺ and I^-. Under optimal conditions, the linear detection ranges were 0.01-20 μM for Hg²⁺ and 0.025-7 μM for I^-, respectively. Meanwhile, the detection limits could be down to 3.3 nM for Hg²⁺ and 8.5 nM for I^-, respectively. Satisfied recoveries had also been gained for measuring Hg²⁺ and I^- in practical water samples. The constructed "on-off-on" fluorescent sensor provided a simple, rapid, robust and reliable platform for detecting Hg²⁺ and I^- in environmental applications.

Bioreduction of Gold Ions under Greener Conditions by the Thiol-Modified M13 Bacteriophage and with Hydroxylamine as the Autocatalytic Reducing Agent

Bioreduction of gold ions by the thiol-modified M13 bacteriophage (M13-SH) has been exploited as the potential alternative to conventional methods based on toxic chemicals, due to the gold affinity of the thiol groups, inherent gold reduction, and high specific surface area of the filamentous virus. Such efforts have been hindered by harsh conditions involving strong reducing agents and extreme pH that are harmful to the virus. Herein, a virus-friendly and greener method of bioreduction of AuCl₄ ^- at neutral pH based on M13-SH is demonstrated. M13-SH was prepared by coupling the virus with N-succinimidyl S-acetylthioacetate, followed by deacylation in the presence of hydroxylamine·HCl to expose the thiol groups. The key finding is that without time-consuming purification, the mixture after deacylation consisting of M13-SH, residual hydroxylamine, and so forth can directly turn ionic gold species into gold, leading to macroscopic precipitated products with interconnected linear structures consisting of fused gold nanoparticles. Besides working as the virus-friendly reducing agent with a unique autocatalytic style, hydroxylamine diminishes disulfide bonding-induced intervirus bundling of M13-SH so as to maintain its efficient biosorption of ionic gold precursors. This work demonstrates a general and green strategy of bioreduction of gold via combination of the gold-affinity proteins or organisms and the unique autocatalytic reduction of hydroxylamine.

Applications, challenges, and needs for employing synthetic biology beyond the lab

Synthetic biology holds great promise for addressing global needs. However, most current developments are not immediately translatable to 'outside-the-lab' scenarios that differ from controlled laboratory settings. Challenges include enabling long-term storage stability as well as operating in resource-limited and off-the-grid scenarios using autonomous function. Here we analyze recent advances in developing synthetic biological platforms for outside-the-lab scenarios with a focus on three major application spaces: bioproduction, biosensing, and closed-loop therapeutic and probiotic delivery. Across the Perspective, we highlight recent advances, areas for further development, possibilities for future applications, and the needs for innovation at the interface of other disciplines.

Fabrication of Bovine Serum Albumin@Au Particles for Colorimetric Detection of Glutathione

Abnormal concentrations of glutathione (GSH) are important indicators of many human diseases such as cancers, liver damage, AIDS, and Alzheimer's disease. In this work, a kind of bovine serum albumin (BSA)@Au core-shell particles were fabricated using 110 nm BSA aggregates as a template, onto which gold shells composed of Au nanoparticles (NPs) were grown through a seeded growth approach. The morphology of the Au shells deposited on BSA aggregates was tuned from sparse to dense distribution of Au NPs by increasing the concentration of silver ions contained in the growth solutions. Surface plasmon resonance (SPR) peaks of BSA@Au particles were tunable in the range from 550 to 620 nm, corresponding to evolution in color from red to blue due to the enhanced plasmonic coupling among the Au NPs in the shell. The blue BSA@Au particles were qualified for colorimetric detection of GSH since GSH may act as a swelling agent for BSA@Au particles by breaking the intermolecular disulfide bonds in BSA aggregates. With an increased amount of GSH presented, the color of BSA@Au particles evolved from blue to red attributed to gradual swelling of BSA@Au particles and thus increased the distance among the Au NPs in the shell, which was readily recognized by naked eyes or recorded by ultraviolet-visible (UV-vis) spectroscopy. This colorimetric method exhibited good selectivity and anti-interference capability in the analysis of GSH in real samples. In addition, a solid sensing system for the detection of GSH was designed and fabricated by dispersing BSA@Au particles into an agarose hydrogel.

Adsorption Mechanisms and Characteristics of Hg2+ Removal by Different Fractions of Biochar

The adsorption mechanisms of mercury ion (Hg2+) by different fractions of biochar were studied, providing a theoretical basis and practical value for the use of biochar to remediate mercury contamination in water. Biochar (RC) was prepared using corn straw as the raw material. It was then fractionated, resulting in inorganic carbon (IC), organic carbon (OC), hydroxyl-blocked carbon (BHC), and carboxyl-blocked carbon (BCC). Before and after Hg2+ adsorption, the biochar fractions were characterized by several techniques, such as energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Obtained results indicate that the reaction mechanisms of RC for Hg2+ removal mainly include electrostatic adsorption, ion exchange, reduction, precipitation, and complexation. The equilibrium adsorption capacity of RC for Hg2+ is 75.56 mg/g, and the adsorption contribution rates of IC and OC are approximately 22.4% and 77.6%, respectively. Despite the lower rate, IC shows the largest adsorption capacity, of 92.63 mg/g. This is attributed to all the mechanisms involved in Hg2+ adsorption by IC, with ion exchange being the main reaction mechanism (accounting for 39.8%). The main adsorption mechanism of OC is the complexation of carboxyl and hydroxyl groups with Hg2+, accounting for 71.6% of the total OC contribution. BHC and BCC adsorb mercury mainly via the reduction–adsorption mechanism, accounting for 54.6% and 54.5%, respectively. Among all the adsorption mechanisms, the complexation reaction of carboxyl and hydroxyl groups with Hg2+ is the dominant effect.