On-site preparation of sandwich plasmonic coupled SERS tape toward pesticide residue determination on food surface.

A sandwich plasmonic coupled surface enhanced Raman spectroscopy (SERS) tape is proposed prepared by peeling the chemical printed silver nanocorals (AgNCs) from Cu sheet with adhesive tape, which can sample targets from food surface and sandwich them between substrates and Cu sheet for SERS detection. The solid-to-solid transformation method for fabricating SERS tapes can effectively avoid the weakening of tape stickiness during the preparation process. The sandwich plasmonic coupled structure of AgNC substrate, targets, and Cu sheet display excellent SERS activity (EF = 1.62 × 107) for sensitive determination of analytes. In addition, due to the high heat conductivity of Cu sheet, the thermal effect of laser irradiation during SERS detection cannot damage the AgNC tapes, which ensures the reproducibility of subsequent quantification. The sandwich plasmonic coupled SERS tape is demonstrated to quantify malachite green (MG) and methyl parathion (MP) with good linear coefficients (> 0.98) by two typical calibration plots under different concentration ranges. The limit of detection (LOD) of the method is 0.17 ng/cm2 and 0.48 µg/cm2 (S/N = 3) for MG and MP. This method can realize the quantitative determination of MP and MG on the surface of fruits and fish scale with recoveries of 93-113%. The satisfactory detection results demonstrate the proposed sandwich plasmonic coupled AgNC tape can be successfully applied to SERS-based point-of-care testing (POCT) for pesticide residue determination, which will provide a new path for designing and constructing SERS tapes.

SERS-Temperature Dual-Mode T-type Lateral Flow Strip for Accurate Detection of Free and Total Prostate-Specific Antigens in Blood.

Accurate point-of-care (POC) analysis of cancer markers is the essence in the comprehensive early screening and treatment of cancer. Dual-mode synchronous detection is one of the effective approaches to reduce the probability of false negatives or false positives. As a result, this can greatly improve the accuracy of diagnosis. In this work, a surface-enhanced Raman scattering (SERS)-temperature dual-mode T-type lateral flow strip was fabricated to direct and simultaneous POC detection of total and free prostate-specific antigens (t-PSA and f-PSA) in blood. With the advantage of high stability of T-type lateral flow strip and simultaneous acquirement of assay results for t-PSA and f:t PSA ratio, the proposed method has high accuracy in the diagnosis of prostate cancer, especially in the diagnostic gray zone between 4.0 and 10.0 ng/mL. The SERS-temperature dual-signal has a good linear correlation with either f-PSA or t-PSA. To evaluate the clinical diagnostic performance of the proposed method, spiked human serum samples and the whole blood sample were analyzed. The assay results showed good recovery, and compared with traditional electrochemiluminescence immunoassay (ECLIA) method (t-PSA: 43.151; f/t ratio: 0.08), the results obtained by the proposed method were similar (t-PSA: 40.15 (SERS), 36.21 (temperature); f/t ratio: 0.08 (SERS), 0.08 (temperature), but the detection time (15 min) and cost ($0.05) had been greatly reduced. Therefore, the proposed SERS-temperature synchronous dual-mode T-type lateral flow strip has a strong application potential in the field of accurate large-scale diagnostics of prostate cancer on-site by simultaneous POC detection of t-PSA and f-PSA in blood.

Facial Preparation of Cyclometalated Iridium (III) Nanowires as Highly Efficient Electrochemiluminescence Luminophores for Biosensing.

In this study, highly efficient ECL luminophores composed of iridium complex-based nanowires (Ir-NCDs) were synthesized via covalently linking bis(2-phenylpyridine)-(4-carboxypropyl-2,2'-bipyridyl) iridium(III) hexafluorophosphate with nitrogen-doped carbon quantum dots (NCDs). The ECL intensity of the nanowires showed a five-fold increase in ECL intensity compared with the iridium complex monomer under the same experimental conditions. A label-free ECL biosensing platform based on Ir-NCDs was established for Salmonella enteritidis (SE) detection. The ECL signal was quenched linearly in the range of 102-108 CFU/mL for SE with a detection limit of 102 CFU/mL. Moreover, the relative standard deviations (RSD) of the stability within and between batches were 0.98% and 3.9%, respectively. In addition, the proposed sensor showed high sensitivity, selectivity and stability towards SE in sheep feces samples with satisfactory results. In summary, the excellent ECL efficiency of Ir-NCDs demonstrates the prospects for Ir(III) complexes in bioanalytical applications.

One-Step, On-Site Chemical Printing of a 3D Plasmon-Coupled Silver Nanocoral Substrate toward SERS-Based POCT.

Surface-enhanced Raman scattering (SERS) with the advantages of high sensitivity, nondestructive analysis, and a unique fingerprint effect shows great potential in point-of-care testing (POCT). However, SERS faces challenges in rapidly constructing a substrate with high repeatability, homogeneity, and sensitivity, which are the key factors that restrict its practical applications. In this study, we propose a one-step chemical printing strategy for synthesizing a three-dimensional (3D) plasmon-coupled silver nanocoral (AgNC) substrate (only need about 5 min) without any pretreatments and complex instruments. The galvanic replacement between AgNO3 and Cu sheets will provide both Ag0 for the formation of silver nanostructures and Cu2+ for the polymerization of fish sperm DNA (FSDNA). The protection of AgNCs is facilitated by the crosslinked FSDNA, which can improve the stability of the substrate and promote the control of its coral-like morphology. The obtained substrate displays excellent capacity of signal enhancement due to the 3D plasmon coupling both between nanocoral tentacles and between nanocorals and Cu sheets as well. Therefore, the AgNC substrates display high activity (enhancement factor = 1.96 × 108) and uniformity (RSD < 6%). Food colorants have been widely used in various foods to improve their color, but the inevitable toxicity of colorants seriously threatens food safety. Therefore, the proposed AgNC substrates were used to directly quantify three kinds of weak-affinity food colorant molecules including Brilliant Blue, Allura Red, and Sunset Yellow assisted by the capture by cysteamine hydrochloride (CA), showing the detection limits (S/N = 3) of 0.053, 0.087, and 0.089 ppm, respectively. The SERS method has been further applied in the detection of the three kinds of food colorants in both complex food samples and urine with recoveries of 91-119%. The satisfactory detection results suggest that the facile preparation strategy of AgNC substrates will be widely used in SERS-based POCT to promote the development of food safety and on-site healthcare.

Noble Metal Single-Atom Catalysts for the Catalytic Oxidation of Volatile Organic Compounds.

Invited for this month's cover is the group of Haifeng Xiong at Xiamen University. The image shows that single-atom catalysts can work in the catalytic oxidation of volatile organic compounds. The Review itself is available at 10.1002/cssc.202102494.

Noble Metal Single-Atom Catalysts for the Catalytic Oxidation of Volatile Organic Compounds.

Volatile organic compounds (VOCs) are detrimental to the environment and human health and must be eliminated before discharging. Oxidation by heterogeneous catalysts is one of the most promising approaches for the VOCs abatement. Precious metal catalysts are highly active for the catalytic oxidation of VOCs, but they are rare and their high price limits large-scale application. Supported metal single-atom catalysts (SACs) have a high atom efficiency and provide the possibility to circumvent such limitations. This Review summarizes recent advances in the use of metal SACs for the complete oxidation of VOCs, such as benzene, toluene, formaldehyde, and methanol, as well as aliphatic and Cl- and S-containing hydrocarbons. The structures of the metal SACs used and the reaction mechanisms of the VOC oxidation are discussed. The most widely used SACs are noble metals supported on oxides, especially on reducible oxides, such as Mn2 O3 and TiO2 . The reactivity of most SACs is related to the activity of surface lattice oxygen of the oxides. Furthermore, several metal SACs show better reactivity and improved S and Cl resistance than the corresponding nanocatalysts, indicating that SACs have potential for application in the oxidation of VOCs. The deactivation and regeneration mechanisms of the metal SACs are also summarized. It is concluded that the application of metal SACs in catalytic oxidation of VOCs is still in its infancy. This Review aims to elucidate structure-performance relationships and to guide the design of highly efficient metal SACs for the catalytic oxidation of VOCs.

Green Synthesis of Three-Dimensional Au Nanorods@TiO2 Nanocomposites as Self-Cleaning SERS Substrate for Sensitive, Recyclable, and In Situ Sensing Environmental Pollutants.

In this work, a simple, low-cost, green, and mild method for the preparation of three-dimensional nanocomposite materials of gold nanorods (Au NRs)@TiO2 is reported. The surface of Au NRs was coated with TiO2 in situ reduction at room temperature without a complicated operation. The synthetic Au NRs@TiO2 nanocomposites were used as surface-enhanced Raman spectroscopy (SERS) active substrates for the reusable and sensitive detection of environmental pollutants. The results showed that the pollutants on Au NRs@TiO2 nanocomposites have higher SERS activity and reproducibility than those on the Au NR substrate without the presence of TiO2. Moreover, the SERS substrate can be readily recycled by UV-assisted self-cleaning to remove residual analyte molecules. Malachite green (MG) and crystal violet (CV) were used as examples to demonstrate the feasibility of the proposed sensor for the sensitive detection of environmental pollutants. The results showed that the limit of detections (LODs) were 0.75 µg/L and 0.50 µg/L for MG and CV, respectively, with the recoveries ranging from 86.67% to 91.20% and 83.70% to 89.00%. Meanwhile, the SERS substrate can be easily regenerated by UV light irradiation. Our investigation revealed that within three cycles, the Au NRs@TiO2 substrates still maintained the high SERS enhancement effect that they showed when first used for SERS detection. These results indicated that the method can be used to detect MG and CV in really complex samples. Due to the high sensitivity, reusability, and portability and the rapid detection property of the proposed sensor, it can have potential applications in the on-site detection of environmental pollutants in a complex sample matrix.

Oil-Free Gold Nanobipyramid@Ag Microgels as a Functional SERS Substrate for Direct Detection of Small Molecules in a Complex Sample Matrix.

Surface-enhanced Raman scattering (SERS) is a super-sensitive analysis technology based on the target molecular fingerprint information. The enhancement of local electromagnetic field of the SERS substrate would increase the target molecules' Raman intensity which adsorb on the surface of nanoparticles. However, the existing adhesive macromolecules in the complex mixed sample would interfere with the adsorption of small target molecules, and it weakens the Raman intensity of target molecules. Microgels are one of the potential materials to suppress the interference of adhesive macromolecules and to avoid the complex pretreatments. However, most of the current microgel synthesis methods involve complex operations with precise instrumentation or the interference of oil and organic reagents. In this work, a simple and oil-free method was proposed to synthesize the gold nanobipyramid (Au NBP)@Ag@hyaluronic acid microgel via the condensation reaction of carboxyl and amino groups. As a proof-of-concept demonstration for small-molecule detection, the rhodamine 6G (R6G) molecules were allowed to enter inside the microgel through the meshes and adsorb on the surface of Au NBP@Ag nanoparticles within 30 min, while the macromolecule (bovine serum albumin in this case) was retained outside the microgel in the meantime. In addition, under the combined action of lightning rod effect of Au NBP and surface plasmon resonance effect of silver render the microgels with high SERS activity. The synthetic Au NBP@Ag@hyaluronic acid microgels were applied to detect 6-thioguanine in the human serum without any pretreatment process, and it showed a high signal enhancement and stable SERS signal, which can satisfy the requirement of clinical diagnosis. These results show that the proposed microgels have potential applications in the field of point-of-care testing.

A universal strategy for the incorporation of internal standards into SERS substrates to improve the reproducibility of Raman signals.

The uneven distribution of metal nanoparticles is a vital influencing factor in the poor uniformity of surface-enhanced Raman scattering (SERS) substrates, which is a challenge in SERS quantitative analysis. Recent reports showed that the reproducibility of a nonuniform SERS substrate can be effectively improved by the use of an internal standard (IS). However, most of these approaches require the investment of time for precise regulation, and those approaches based on the addition of an IS are specific to a certain substrate. In this work, we proposed a simple, rapid and universal method to incorporate an IS into a SERS substrate for improving the reproducibility of Raman signals based on the systematic evaluation of the influencing factors of the competitive adsorption between the IS and the target analytes. Following the proposed pressure drop-coating (PDC) method, an IS-modified gold nanobipyramids (Au NBPs)/anodic aluminum oxide (AAO) SERS substrate was fabricated within 1 min, showing high reproducibility of Raman signals. In addition, the IS-modified Au NBPs/AAO SERS substrate was successfully applied to analyze thiram in freshly squeezed apple juice and the result showed a stable Raman signal with a relative standard deviation of less than 6.00%. What is more, three different commercial SERS chips were modified with an IS molecule using the PDC method. Compared to the traditional SERS chips, the Raman signal reproducibility of the functionalized SERS chips was improved significantly. Since the addition of an IS is not based on a certain substrate, the proposed approach could be useful for all the researchers working in the field of SERS.

Facile Fabrication of a Functional Filter Tip for Highly Efficient Reduction of Nicotine Content in Mainstream Smoke.

The nicotine addiction problem is of great concern, particularly in adolescents. Notably, nicotine addiction drives humans to continue smoking. Notably, several diseases and disorders are caused by smoking. To date, various adsorbents have been proposed to develop a functionalization filter tip for reducing nicotine content in mainstream smoke. However, the nicotine adsorption efficiencies of most of the reported functionalization filter tips were not satisfactory, and their preparation process was complex and time-consuming. Herein, we demonstrate a highly active and adsorbing filter tip for cigarettes, fabricated by decorating polydopamine (PDA) on the surface of a commercial filter tip in situ. The PDA coating on the filter tip was obtained by the self-polymerization of dopamine (DA) within 16 h, which was quicker and easier than the preparation processes of other reported functionalized filter tips. Significantly, the PDA-decorated filter tip had a nicotine adsorption efficiency as high as ∼95%, which was much higher than most of the commercial filter tips.

Nickel-phosphate pompon flowers nanostructured network enables the sensitive detection of microRNA.

An electrochemical immuno-nanogenosensor is developed based on noble-metal-free nickel phosphate nanostructure (NiPNs) as an excellent biocompatible material for miRNA detection in blood serum and urine samples without using indicators for the first time. The pompon flower-like morphology of NiPNs is synthesized, and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction pattern (XRD), fourier transform-infrared spectroscopy (FT-IR), and electrochemical impedance methods. The novel NiPNs nanostructured interface was constructed by coordinate covalent bonding between Ni and phosphate group of probe DNA. The constructed NiPNs-p-DNA surface served as the amplified hybridization platform enabling efficient access to numerous target microRNA sequences. As a result, the developed NiPFNs biosensing platform displayed excellent sensitivity, selectivity, and ultralow experimental limit-of-detection (LOD) of 0.034 pM (S/N = 3) as compared with other Ni phosphide nanostructures. This simple and efficient approach is highly suitable for the development of point-of-care detection systems. To the extent of our knowledge, this is the first report on trace level detection of miRNAs employing non-noble Ni metal nanostructures based biosensing platform.

On-spot surface enhanced Raman scattering detection of Aflatoxin B1 in peanut extracts using gold nanobipyramids evenly trapped into the AAO nanoholes.

Simple, rapid, convenient, and economical surface enhanced Raman scattering (SERS) substrate is developed for on-site evaluation of Aflatoxin B1 (AFB1) in food matrix using handheld Raman Spectrometer. Self-assembly of gold nanobipyramids (Au NBPs) into the nanoholes of anodic aluminum oxide (AAO) template/pattern using 'drop-dry' approach provides a reliable pathway for the rapid fabrication of highly active and uniform SERS substrate. It shows enhanced and reproducible SERS signals towards the probe molecule, 4-aminothiophenol (4-ATP) with a relative standard deviation (RSD) of less than 10% and an average enhancement factor (EF) of 1 × 108. For practical application, the proposed method is demonstrated for the detection of aflatoxin B1 (AFB1) in peanut extracts. The results show that the AFB1 in peanut extracts can be identified within 1 min, with a limit of detection of 0.5 µg/L. Compared with conventional ELISA based AFB1 analysis, our method is much more efficient (1 min versus >30 min).

A Facile Approach for On-Site Evaluation of Nicotine in Tobacco and Environmental Tobacco Smoke.

Nicotine is highly addictive and harmful. It is one of the main active ingredients in tobacco and a major pollutant in environmental tobacco smoke. Thus, it is important to detect the nicotine content in tobacco and to monitor the nicotine content in environmental tobacco smoke. However, until present, there still has been no effective device for on-site determination of nicotine content in tobacco and environmental tobacco smoke. In this work, a portable device is fabricated for sensitive on-site evaluation of nicotine in tobacco and environmental tobacco smoke based on surface-enhanced Raman scattering (SERS). The weight of the entire device is less than 1 kg, and it uses a chargeable battery to drive both the pump and the Raman spectrometer. The total analysis time can be completed within 3-5 min. Thus, it has great potential for on-site analysis of nicotine in tobacco and environmental tobacco smoke.

Rapid synthesis of a highly active and uniform 3-dimensional SERS substrate for on-spot sensing of dopamine.

A rapid method is described for the preparation of a highly uniform and sensitive SERS substrate by an improved 'drop-and-dry' method. Gold nanobipyramids (Au NBPs) were prepared inside the nanoholes (nanowalls) of anodic aluminum oxide (AAO) templates with a typically 5-µm nanohole depth. The SERS substrate can be prepared by this method within 40 s and on large scale. The SERS signals obtained with this Au NBPs-AAO substrate is stronger by four-orders of magnitude compared to conventional a silicon wafer substrate. The SERS signal for dopamine (DA; measured at 1311 cm-1) is found to be enhanced by a factor of 2.2 × 108. The response to DA extends from 10 nM to 0.1 mM, and the limit of detection is 6.5 nM (at S/N = 3). The assay was applied to the determination of DA in spiked human serum. Graphical abstract Schematic presentation of a highly active and uniform 3-dimensional substrate composed of gold nanobipyramids and anodic aluminum oxide (Au NBP/AAO). It was used for on-spot sensing of dopamine.