Porous organic polymers assisted aptamer signal amplification for enhanced photoeletrochemical detection of MUC1.

Mucin1 (MUC1) is an extensively glycosylated transmembrane protein that is widely distributed and overexpressed on the surface of cancer cells, playing an important role in tumor occurrence and metastasis. Therefore, highly sensitive detection of MUC1 is of great significance for early diagnosis, treatment monitoring, and prognosis of cancer. Here, an ultra-sensitive photoelectrochemical (PEC) sensing platform was developed based on an aptamer amplification strategy for highly selective and sensitive detection of MUC1 overexpressed in serum and on cancer cell surfaces. The sensing platform utilized copper phthalocyanine to fabricate porous organic polymers (CuPc POPs), and was effectively integrated with g-C3N4/MXene to form a ternary heterojunction material (g-C3N4/MXene/CuPc POPs). This material effectively improved electron transfer capability, significantly enhanced light utilization, and greatly enhanced photoelectric conversion efficiency, resulting in a dramatic increase in photocurrent response. MUC1 aptamer 1 was immobilized on a chitosan-modified photoelectrode for the selective capture of MUC1 or MCF-7 cancer cells. When the target substance was present, MUC1 aptamer 2 labeled with methylene blue (MB) was specifically adsorbed on the electrode surface, leading to enhanced photocurrent. The concentration of MUC1 directly correlated with the number of MB molecules attracted to the electrode surface, establishing a linear relationship between photocurrent intensity and MUC1 concentration. The PEC biosensor exhibited excellent sensitivity for MUC1 detection with a wide detection range from 1 × 10-7 to 10 ng/mL and a detection limit of 8.1 ag/mL. The detection range for MCF-7 cells was from 2 × 101 to 2 × 106 cells/mL, with the capability for detecting single MCF-7 cells. The aptamer amplification strategy significantly enhanced PEC performance, and open up a promising platform to establish high selectivity, stability, and ultrasensitive analytical techniques.

Recyclable Au@R-Fe3O4/g-C3N4 substrates for rapid SERS detection and degradation of multiple pollutants.

Developing a Surface-enhanced Raman spectroscopy (SERS) method with excellent detecting ability, good recyclability and analyzing multiple pollutants rapidly are critical for evaluation of water quality in emergency pollution affairs. While constructing a multifunctional substrate with these characteristics to realize the application of SERS in water quality monitoring remains a challenge. In this work, a reusable Au@R-Fe3O4/g-C3N4 SERS substrate is prepared by loading Au nanoparticles (Au NPs) on Fe3O4 nanorings (R-Fe3O4) and the formed Au@R-Fe3O4 is further combined with g-C3N4 nanosheets through a simple electrostatic assembly method. The Au@R-Fe3O4/g-C3N4 nanocomposite presents multifunction of magnetic enrichment, SERS signal enhancement, multiple pollutants analyzing, and photocatalytic activity, which achieves quantitative detection of rhodamine B (RhB), tetracycline hydrochloride (TC), and 4-chlorophenol (4-CP), with detection limits of 5.30 × 10-9, 7.50 × 10-8, 7.69 × 10-8 mol/L, respectively. Furthermore, the recyclable detection capability of Au@R-Fe3O4/g-C3N4 for multi components is demonstrated by the strong SERS signal after 9 cycles of "detection-degradation" processes. Combined with good uniformity and stability, this SERS method based on Au@R-Fe3O4/g-C3N4 substrate provides a new strategy for the multi-pollutants detection and degradation in water environment.

Reticular chemistry guided precise construction of zirconium-pentacarboxylate frameworks with 5-connected Zr6 clusters.

Zirconium-based metal-organic frameworks (Zr-MOFs) have been extensively studied due to their very rich structural chemistry. The combination of nearly unlimited carboxylic acid-based linkers and Zr6 clusters with multiple connectivities has led to diverse structures and specific properties of resultant Zr-MOFs. Herein, we demonstrate the successful use of reticular chemistry to construct two novel Zr-MOFs, HIAM-4040 and HIAM-4040-OH, with zfu topology. Based on a thorough structural analysis of (4,4)-connected lvt-type Zr-tetracarboxylate frameworks and a judicious linker design, we have obtained the first example of a Zr-pentacarboxylate framework featuring unprecedented 5-connected organic linkers and 5-connected Zr6 clusters. Compared with HIAM-4040, a larger Stokes shift is achieved in HIAM-4040-OH via hydroxyl group induced excited-state intramolecular proton transfer (ESIPT). HIAM-4040-OH exhibits high chemical and thermal stability and is used for HClO detection in aqueous solution with excellent sensitivity and selectivity.

Ultrabright Green-Emissive Nanodots for Precise Biological Visualization.

Developing general methods to fabricate water-dispersible and biocompatible fluorescent probes will promote different biological visualization applications. Herein, we report a metal-facilitated method to fabricate ultrabright green-emissive nanodots via the one-step solvothermal treatment of rose bengal, ethanol, and various metal ions. These metal-doped nanodots show good water dispersity, ultrahigh photoluminescence quantum yields (PLQYs) (e.g., the PLQY of Fe-doped nanodots (FeNDs) was ∼97%), and low phototoxicity. Owing to the coordination effect of metal ions, the FeNDs realize glutathione detection with outstanding properties. Benefiting from the high endoplasmic reticulum (ER) affinity of the chloride group, the FeNDs can act as an ER tracker with long ER imaging capacity (FeNDs: >24 h; commercial ER tracker: ∼1 h) and superb photostability and can achieve tissue visualization in living Caenorhabditis elegans. The metal-doped nanodots represent a general nanodot preparation method and may shed new light on diverse biological visualization uses.

Reticular Chemistry with Art: A Case Study of Olympic Rings-Inspired Metal-Organic Frameworks.

Herein, we demonstrate the successful utilization of reticular chemistry as an excellent designing strategy for the deliberate construction of a zirconium-tetracarboxylate metal-organic framework (MOF) inspired by the Olympic rings. HIAM-4017, with an unprecedented (4,8)-c underlying net topology termed jcs, was developed via insightful reconstruction of the rings and judicious design of a nonsymmetric organic linker. HIAM-4017 exhibits high porosity and excellent chemical and thermal stability. Furthermore, excited-state intramolecular proton transfer (ESIPT) was achieved in an isoreticular MOF, HIAM-4018, with a large Stokes shift of 155 nm as a result of introducing the hydroxyl group to the linker skeleton to induce OH···N interactions. Such interactions were analyzed thoroughly by employing the time-dependent density functional theory (TD-DFT). Because of their good thermal and chemical stability, and strong luminescence, nanosized HIAM-4017 and HIAM-4018 were fabricated and used for Cr2O72- detection. Both MOFs demonstrate excellent sensitivity and selectivity. This work represents a neat example of building structure- and property-specific MOFs guided by reticular chemistry.

Nanozyme-mediated signal amplification for ultrasensitive photoelectrochemical sensing of Staphylococcus aureus based on Cu-C3N4-TiO2 heterostructure.

Food-borne pathogens are one of the leading causes of food poisoning, which vigorously affect food safety and human health. Therefore, the development of early and rapid detection methods for food pollution evaluation is the key to food safety and quality control. Herein, a simple and inexpensive photoelectrochemical (PEC) sensor is developed for highly selective and ultrasensitive detection of Staphylococcus aureus (S. aureus). The technique is based on "signal-off" that employs Cu-C3N4-TiO2 heterostructures as photoactive materials and monolayer Cu-C3N4 nanozyme as a signal amplifier. In the presence of S. aureus, the aptamer-modified Cu-C3N4 (Cu-C3N4@Apt, a signal amplifier) and S. aureus were specifically anchored on the surface of the ligand-modified photoelectrode. The Cu-C3N4@Apt nanozyme acted as a peroxidase to catalyze the oxidation of 4-chloro-1-naphthol (4-CN) to produce insoluble precipitate on the electrode surface and resulted in a significant decrease in photocurrent. Based on the signal-amplification by the Cu-C3N4@Apt nanozyme, the constructed PEC sensor demonstrated a wide linear range between 10-108 CFU/mL for the S. aureus detection with the detection limit (LOD) as low as 3.40 CFU/mL. Furthermore, the PEC sensor was capable of determining S. aureus in spiked orange juice and milk, with the recovery of 91%-113%, indicating the reliability of the sensor for S. aureus detection in real samples. This investigation provides a feasible strategy for the design of highly selective and ultrasensitive PEC sensors to determine analytes in complex systems.

Ultrasensitive SERS detection of exhaled biomarkers of lung cancer using a multifunctional solid phase extraction membrane.

The construction and clinical application of a surface-enhanced Raman scattering (SERS) platform for the early diagnosis of lung cancer could improve the survival rate of patients and would be of great significance. Nevertheless, a sensitive and reusable method for the detection of aldehydes, as biomarkers of lung cancer, in exhaled breath is still an enormous challenge. Aldehydes generally have a low cross section in Raman scattering and have a weak specific affinity to plasmonic nanoparticle surfaces, meaning that sensing them at low concentrations is incredibly difficult. Herein, an ultrasensitive SERS strategy, that can be recycled for further use, for the detection of lung cancer biomarkers in the form of aldehydes was realized by fabrication of a multifunctional Ag NPs@ZIF-67/g-C3N4 solid phase extraction (SPE) membrane. Based on the change in the vibrational fingerprints of 4-ATP before and after reaction with the aldehydes, the SPE membrane was successfully used for the ultrasensitive detection of aldehydes with a detection limit of 1.35 nM. The excellent SERS performance was attributed to the synergistic effect of the densely and closely distributed Ag NPs (providing SERS "hot spots"), ZIF-67 (concentrating the analyte molecules) and g-C3N4 (forming a membrane to prolong the contact time between the aldehydes and the substrate). In addition, recycling of the SPE membrane was achieved by utilizing the self-cleaning ability of the Ag NPs@ZIF-67/g-C3N4 membrane originating from the photocatalytic properties of g-C3N4. The proposed SERS membrane was easy to operate, rapid and portable, thus providing a potential tool for a point-of-care test in clinical and diagnostic practice.

Recent advances in graphene nanoribbons for biosensing and biomedicine.

In recent years, a new type of quasi-one-dimensional graphene-based material, graphene nanoribbons (GNRs), has attracted increasing attention. The limited domain width and rich edge configurations of GNRs endow them with unique properties and wide applications in comparison to two-dimensional graphene. This review article mainly focuses on the electrical, chemical and other properties of GNRs, and further introduces the typical preparation methods of GNRs, including top-down and bottom-up strategies. Then, their biosensing and biomedical applications are highlighted in detail, such as biosensors, photothermal therapy, drug delivery, etc. Finally, the challenges and future prospects in the synthesis and application of functionalized GNRs are discussed. It is expected that GNRs will have significant practical use in biomedical applications in the future.

Combined Paper Centrifugal Chromatographic Separation and SERS Detection for Multicomponent Substances.

The separation and chemical analysis of mixtures in an emergency situation represent major challenges, especially in remote or poverty-stricken areas. A novel method was developed for the rapid separation and detection of multiple components via paper centrifugal chromatography, which costs as little as $2.26 US. The method was realized based on the combination of portable paper centrifugal chromatography and surface-enhanced Raman scattering (SERS) detection. This coupled technique was successfully implemented for the separation and qualitative analysis of a rhodamine 6G-crystal violet mixture and a colorless aniline-pyrocatechol-benzidine mixture. A chromatographic mobile phase was collected using absorbent cotton, which was demonstrated to have no effect on the SERS results. The optimized device achieved rapid and effective separation of the colorless aniline-pyrocatechol-benzidine mixture with a high centrifugal force (0.3303π2 N). The newly developed method involving multicomponent paper centrifugal chromatography-SERS detection will be of great value for emergency-related substance separation and analysis in remote and poor areas.

In situ food-borne pathogen sensors in a nanoconfined space by surface enhanced Raman scattering.

The incidence of disease arising from food-borne pathogens is increasing continuously and has become a global public health problem. Rapid and accurate identification of food-borne pathogens is essential for adopting disease intervention strategies and controlling the spread of epidemics. Surface-enhanced Raman spectroscopy (SERS) has attracted increasing interest due to the attractive features including simplicity, rapid measurement, and high sensitivity. It can be used for rapid in situ sensing of single and multicomponent samples within the nanostructure-based confined space by providing molecular fingerprint information and has been demonstrated to be an effective detection strategy for pathogens. This article aims to review the application of SERS to the rapid sensing of food-borne pathogens in food matrices. The mechanisms and advantages of SERS, and detection strategies are briefly discussed. The latest progress on the use of SERS for rapid detection of food-borne bacteria and viruses is considered, including both the labeled and label-free detection strategies. In closing, according to the current situation regarding detection of food-borne pathogens, the review highlights the challenges faced by SERS and the prospects for new applications in food safety. Graphical abstract In this review, the advances on the SERS detection of pathogens over the past decades have been reviewed, focusing on the improvements in sensitivity, reproducibility, specificity, and the performance of the SERS-based assay in complex analytical scenarios.

A disposable paper-based hydrophobic substrate for highly sensitive surface-enhanced Raman scattering detection.

Detection of target analytes with high sensitivity and reproducibility remains a challenge for surface-enhanced Raman scattering (SERS) due to the lack of cost-effective and highly sensitive substrates. In this study, a hydrophobic SERS substrate capable of concentrating nanoparticles and analytes was prepared by spin-coating lubricating liquid onto commercial paper. The condensation effect of the paper-based hydrophobic substrate induced aggregation of gold nanoparticles (Au NPs) to generate ''hot spots'' for SERS and to drive analytes to the hot-spot areas for more sensitive detection. The obtained SERS signal intensity was 5-fold higher than that obtained using common paper, and a detection limit (LOD) of 4.3 × 10-10 M for rhodamine 6G (R6G) was achieved. Randomly selected points on the substrate and different batches of substrates all exhibited high reproducibility, and the relative standard deviation (RSD) at 1362 cm-1 is approximately 11%. A further application of the hydrophobic substrate was demonstrated by the detection of cytochrome C within a linear detection range of 3.90 × 10-8 M-1.25 × 10-6 M. In addition, the prepared substrate can obtain identifiable SERS spectra of cancer cells and non-cancer cells because a large number of AuNP or Au NPs clusters can adhere to cells, resulting in the construction of a 3D hotspot matrix. The disposable hydrophobic paper substrate eliminates the problem of solution diffusion, and also provides an effective platform for biomolecular screening detection.

Fabrication of paper-based SERS substrates by spraying silver and gold nanoparticles for SERS determination of malachite green, methylene blue, and crystal violet in fish.

A disposable surface-enhanced Raman scattering (SERS) substrate was prepared by successively spraying silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) onto commercial filter paper using an inexpensive consumer sprayer. The strong surface enhancement of AgNPs and chemical stability of AuNPs can be advantageously combined. The substrate exhibited excellent SERS activity for malachite green (MG), methylene blue (MB), and crystal violet (CV) under 785-nm excitation, with limits of detection (LODs) of 4.3 × 10-9, 2.0 × 10-8, and 8.1 × 10-8 M, respectively. The substrate exhibited long-term stability, and it can be stored under ambient conditions for 4 weeks with a relative standard deviation of less than 3% among peak intensities. The substrate also showed good reproducibility with a relative standard deviation of 7.1% among different substrate peak intensities. The substrates enable on-site determination of residual fishery drugs and distinguish MG, MB, and CV mixtures in spiked fish within 5 min, and the average recoveries in fish scales and fish meat were better 90.1% and 76.9%, respectively. The method exhibited rapidity, simplicity, and high sensitivity and is expected to be used for the screening of additives in food.

Extraction of Two-Dimensional Aluminum Alloys from Decagonal Quasicrystals.

Atomically thin metallic alloys are receiving increased attention due to their prospective applications as interconnects/contacts in two-dimensional (2D) circuits, sensors, and catalysts, among others. In this work, we demonstrate an easily scalable technique for the synthesis of 2D metallic alloys from their 3D quasicrystalline precursors. We have used aluminum (Al)-based single-phase decagonal quasicrystal Al66Co17Cu17 alloy to extract the corresponding 2D alloy structure. The 2D layered Al alloy possesses 2-fold decagonal quasicrystalline symmetry and consists of two- or three-layer-thick sheets with a lateral dimension of microns. These 2D metallic layers were combined with the atomic layers of tungsten disulfide to form the stacked heterostructures, which is demonstrated to be a stable and efficient catalyst for hydrogen evolution reaction.

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The phosphate-solubilizing medium plate screening and heavy metal resistance rescreening were used to isolate a phosphate-solubilizing bacterium (coded ZLT11) from the rhizosphere of Mikania micrantha. Results from 16S rRNA gene sequence analysis revealed that the strain ZLT11 belonged to Paenibacillus sp. The amount of phosphorus solubilized from calcium phytate and phytic acid by the ZLT11 was 84.10 and 73.84 mg·L-1, respectively. The maximum phosphate solubilizing activity to calcium phytate (95.66 mg·L-1) was at 30 ℃ and initial pH 9.0. The strain ZLT11 displayed the tolerance to ≤ 400 mg·L-1 Pb 2+, ≤ 100 mg·L-1 Cd 2+, and ≤ 40 mg·L-1 Hg 2+. With calcium phytate as phosphorus source, the inoculation strain ZLT11 treatment increased the average root length, root number, seedling height and total biomass of rice seedlings by 106.7%, 76.6%, 49.0% and 46.3%, respectively. The strain ZLT11 could improve rice seedlings growth under Cd stress.

Sensitive detection of telomerase activity in cells using a DNA-based fluorescence resonance energy transfer nanoprobe.

Telomerase activity is inhibited in normal somatic cells but abnormally high in the majority of cancer cells. Maintenance of active telomerase in cancer cells promotes proliferation and immortalization. With the difference in telomerase activity between cancer and normal cells in mind, we designed a nanoprobe based on quantum dot (QD) and fluorescence resonance energy transfer (FRET). The nanoprobe consisted of a specific sequence of DNA with the two ends labeled with QD as a fluorescent donor and Alexa488 as a fluorescent acceptor, respectively. FRET signal tracking was performed by adjusting the distance between donors and acceptors, and changes in the FRET signal shown to be related to telomerase activity. Incubation of cells with the nanoprobe facilitated sensing of intracellular telomerase activity, and consequent discrimination between normal and cancer cells. Our novel DNA nanoprobe based on QD-FRET achieved sensitive detection of telomerase in cells up to a detection limit of one cell, and quantitative detection of telomerase activity in different numbers of cells. The nanoprobe generated in this study is expected to allow dynamically monitoring of the changes in telomerase activity in cells under treatment with drugs, providing a potential basis for early diagnosis and management of cancer.

Recyclable three-dimensional Ag nanorod arrays decorated with O-g-C3N4 for highly sensitive SERS sensing of organic pollutants.

A three-dimensional (3D) substrate was developed by assembling a monolayer of graphitic carbon nitride (O-g-C3N4) on Ag nanorod arrays (Ag NRs) for sensitive and recyclable surface enhanced Raman scattering (SERS) detection. The prepared Ag NRs/O-g-C3N4 substrate not only generated a significant Raman enhancement effect as a result of the strong π-π stacking interaction between O-g-C3N4 and the analytes but also possessed excellent self-cleaning property via visible-light irradiation that was attributed to its outstanding catalytic performance. Highly sensitive SERS detection could be achieved with a LOD of 8.2 × 10-10 M for R6 G, and the substrate could be used repeatedly for at least four cycles with tolerable intensity attenuation. In addition, the 3D substrate exhibited long-term stability originating from the electron-donor effect of O-g-C3N4 and high reproducibility due to the uniform decoration of O-g-C3N4 on the Ag NRs through the strong interaction. Furthermore, using Ag NRs/O-g-C3N4, the recyclable detection of antibiotics in a water sample was demonstrated with high sensitivity, which indicates that the 3D Ag NRs/O-g-C3N4 substrate is a promising candidate for eliminating the challenges of single-use SERS substrates and building a portable SERS platform to sense organic molecular species.

Thin layer chromatography combined with surface-enhanced raman spectroscopy for rapid sensing aflatoxins.

A fast and facile method was developed for on-site detection of aflatoxins (AFs) in moldy agricultural products using thin layer chromatography combined with surface-enhanced Raman spectroscopy (TLC-SERS). Four different AFs were successfully separated by TLC and then a small portable Raman spectrometer, with gold colloids as the SERS-active substrate, was applied to identify the separated spots. TLC-SERS application to on-site detection of AFs was systematically investigated. Qualitative and quantitative AF detection was found to be easily accomplished and limits of detection were estimated to be 1.5 × 10-6, 1.1 × 10-5, 1.2 × 10-6, and 6.0 × 10-7 M for AFB1, AFB2, AFG1, and AFG2, respectively. The proposed method was also highly selective, enabling successful AF identifications in complex extracts from moldy peanuts. The study showed that TLC-SERS could be effectively used for separation and detection of these four AFs, demonstrating good prospects for on-site qualitative screening of agricultural products.

Facile fabrication of ternary TiO2-gold nanoparticle-graphene oxide nanocomposites for recyclable surface enhanced Raman scattering.

A bi-functional ternary nanocomposite was developed by decorating TiO2 and gold nanoparticles on the reduced graphene oxide nanosheets (TiO2-Au-rGO) for recyclable surface enhanced Raman scattering (SERS) detection. TiO2-Au-rGO nanocomposites have been shown to demonstrate the superior SERS performances, which can be used for highly sensitive detection of rhodamine 6 G with a limit of detection of 1.2 × 10-10 M. Subsequently, the surface can be cleaned automatically by the photocatalytic degradation of the adsorbed analytes into inorganic small molecules under visible light irradiation. This can be attributed to the excellent photocatalytic degradation ability, leading to a recyclable SERS application. After being used four times, their excellent SERS and catalytic performances can still be retained. These results suggest that the TiO2-Au-rGO nanocomposites can provide a new strategy for fabricating recyclable SERS substrates, which are highly desirable for SERS practical application.

Removal of Antibiotics From Water with an All-Carbon 3D Nanofiltration Membrane.

Recent industrial developments and increased energy demand have resulted in significantly increased levels of environmental pollutants, which have become a serious global problem. Herein, we propose a novel all-carbon nanofiltration (NF) membrane that consists of multi-walled carbon nanotubes (MWCNTs) interposed between graphene oxide (GO) nanosheets to form a three-dimensional (3D) structure. The as-prepared membrane has abundant two-dimensional (2D) nanochannels that can physically sieve antibiotic molecules through electrostatic interaction. As a result, the prepared membrane, with a thickness of 4.26 µm, shows both a high adsorption of 99.23% for tetracycline hydrochloride (TCH) and a high water permeation of 16.12 L m- 2 h- 1 bar- 1. In addition, the cationic dye methylene blue (MB) was also removed to an extent of 83.88%, indicating broad applications of the prepared membrane.

Highly Reproducible Ag NPs/CNT-Intercalated GO Membranes for Enrichment and SERS Detection of Antibiotics.

The increasing pollution of aquatic environments by antibiotics makes it necessary to develop efficient enrichment and sensitive detection methods for environmental antibiotics monitoring. In this work, silver nanoparticles and carbon nanotube-intercalated graphene oxide laminar membranes (Ag NPs/CNT-GO membranes) were successfully prepared for enrichment and surface-enhanced Raman scattering (SERS) detection of antibiotics. The prepared Ag NPs/CNT-GO membranes exhibited a high enrichment ability because of the π-π stacking and electrostatic interactions of GO toward antibiotic molecules, which enhanced the sensitivity of SERS measurements and enabled the antibiotics to be determined at sub-nM concentrations. In addition, the nanochannels created by the intercalation of CNTs into GO layers resulted in an 8-fold enhancement in the water permeance of Ag NPs/CNT-GO membranes compared to that of pure GO membranes. More importantly, the Ag NPs/CNT-GO membranes exhibited high reproducibility and long-term stability. The spot-to-spot variation in SERS intensity was less than 15%, and the SERS performance was maintained for at least 70 days. The Ag NPs/CNT-GO membranes were also used for SERS detection of antibiotics in real samples; the results showed that the characteristic peaks of antibiotics were obviously recognizable. Thus, the sensitive SERS detection of antibiotics based on Ag NPs/CNT-GO offers great potential for practical applications in environmental analysis.