ReS2 Nanoflowers-Assisted Confined Growth of Gold Nanoparticles for Ultrasensitive and Reliable SERS Sensing.

ReS2, as a new member of transition metal dichalcogenides (TMDCs), has emerged as a promising substrate for semiconductor surface-enhanced Raman spectroscopy (SERS) due to its unique optoelectronic properties. Nevertheless, the sensitivity of the ReS2 SERS substrate poses a significant challenge to its widespread application in trace detection. In this work, we present a reliable approach for constructing a novel ReS2/AuNPs SERS composite substrate, enabling ultrasensitive detection of trace amounts of organic pesticides. We demonstrate that the porous structures of ReS2 nanoflowers can effectively confine the growth of AuNPs. By precisely controlling the size and distribution of AuNPs, numerous efficient and densely packed "hot spots" were created on the surface of ReS2 nanoflowers. As a result of the synergistic enhancement of the chemical and electromagnetic mechanisms, the ReS2/AuNPs SERS substrate demonstrates high sensitivity, good reproducibility, and superior stability in detecting typical organic dyes such as rhodamine 6G and crystalline violet. The ReS2/AuNPs SERS substrate shows an ultralow detection limit of 10-10 M and a linear detection of organic pesticide molecules within 10-6-10-10 M, which is significantly lower than the EU Environmental Protection Agency regulation standards. The strategy of constructing ReS2/AuNPs composites would contribute to the development of highly sensitive and reliable SERS sensing platforms for food safety monitoring.

Design and Simulation of a Ratiometric SPR Sensor Based on a 2D van der Waals Heterojunction for Refractive Index Measurement.

Surface plasmon resonance (SPR) sensors have been widely applied in many fields because of their advantages of working in real time and high sensitivity. However, because the spectrum of an SPR sensor is easily affected by the smoothness of the metal surface, this type of sensor has obvious disadvantages in the application of quantitative detection. We designed an SPR refractive index sensor for molecular detection that has the advantage of quantifiability. A ratio spectral quantitative analysis method was established based on the two coherent dips of the SPR spectrum formed by the strong coupling effect between the surface plasmon polaritons and the excitons of the J-aggregate molecule 5,6-dichloro-2-[3-[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)-2-benzimidazoline subunit] propenyl]-3-ethyl-1-(4-sulfobutyl) benzimidazole hydroxide inner salt (TDBC). The introduced MoS2/graphene van der Waals heterojunction produced an effective charge transfer to the Ag film, resulting in significant electric field enhancement at the sensing interface and further improving the detection sensitivity of the sensor. The simulation results showed that for 43 nm Ag film, for example, the ratiometric SPR sensor with the Ag film structure can obtain 16.12 RIU-1 sensing sensitivity, applied to the detection of gas molecules, while the SPR sensor with single-layer graphene and three layers of MoS2 heterostructures can obtain 50.68 RIU-1 sensing sensitivity. The addition of van der Waals heterostructures can significantly improve sensing performance by 215%.

Fluorine-Nitrogen-Codoped Carbon Dots as Fluorescent Switch Probes for Selective Fe(III) and Ascorbic Acid Sensing in Living Cells.

High-quality fluorescent probes based on carbon dots (CDs) have promising applications in many fields owing to their good stability, low toxicity, high quantum yield, and low raw material price. The fluorine- and nitrogen-doped fluorescent CDs (NFCDs) with blue fluorescence was successfully synthesized using 3-aminophenol and 2,4-difluorobenzoic acid as the raw material by the hydrothermal method. The NFCDs as probe can be used to directly and indirectly detect Fe3+ (detection range: 0.1-150 µM and detection limit: 0.14 µM) and ascorbic acid (AA) (detection range: 10-80 µM and detection limit: 0.11 µM). The NFCDs-based probe shows exceptional selectivity and strong anti-interference for Fe3+ and ascorbic acid (AA). In addition, we examined the response of NFCDs to Fe3+ and AA in living cells, which showed that the timely use of AA can reduce the effects of iron poisoning. This has important biological significance. This means that using NFCDs as fluorescent probes is beneficial for Fe3+ and AA detection and observing their dynamic changes in living cells. Thus, this work may contribute to the study of Fe3+- and AA-related diseases.

Bifunctional Nitrogen and Fluorine Co-Doped Carbon Dots for Selective Detection of Copper and Sulfide Ions in Real Water Samples.

Copper ions (Cu2+) and sulfur ions (S2-) are important elements widely used in industry. However, these ions have the risk of polluting the water environment. Therefore, rapid and quantitative detection methods for Cu2+ and S2- are urgently required. Using 2,4-difluorobenzoic acid and L-lysine as precursors, nitrogen and fluorine co-doped dots (N, F-CDs) were synthesized in this study via a hydrothermal method. The aqueous N, F-CDs showed excellent stability, exhibited satisfactory selectivity and excellent anti-interference ability for Cu2+ detection. The N, F-CDs, based on the redox reactions for selective and quantitative detection of Cu2+, showed a wide linear range (0-200 µM) with a detection limit (215 nM). By forming the N, F-CDs@Cu2+ sensing platform and based on the high affinity of S2- to Cu2+, the N, F-CDs@Cu2+ can specifically detect S2- over a linear range of 0-200 µM with a detection limit of 347 nM. In addition, these fluorescent probes achieved good results when used for Cu2+ and S2- detection in environmental water samples, implying the good potential for applications.

Nitrogen-doped carbon dots with high selectivity for hydrosulfide sensing and their living cells imaging.

Hydrosulfuric acid is an aqueous solution of hydrogen sulfide (H2S). At physiological pH, approximately 80% of the total amount of H2S exists in the form of monoanionic HS-. Because HS- is both widely distributed and highly toxic to humans, it is necessary to design an efficient method to detect HS- with high sensitivity and selectivity. So, the nitrogen-doped carbon dots (NCDs) with green fluorescence are synthesized using a one-step hydrothermal method. The as-prepared NCDs show it can be effectively used as an indicator for monitoring HS-. And the NCD fluorescence intensity exhibits a linear relationship with HS- concentration. In addition, NCDs as a probe can be applied for fluorescence imaging in living cells to detect the presence of trace exogenous HS-.

Sensitive determination of dopamine levels via surface-enhanced Raman scattering of Ag nanoparticle dimers.

BACKGROUND: Dopamine (DA) is an important neurotransmitter in the hypothalamus and pituitary gland, which can produce a direct influence on mammals' emotions in midbrain. Additionally, the level of DA is highly related with some important neurologic diseases such as schizophrenia, Parkinson, and Huntington's diseases, etc. In light of the important roles that DA plays in the disease modulation, it is of considerable significance to develop a sensitive and reproducible approach for monitoring DA. PURPOSE: The objective of this study was to develop an efficient approach to quantitatively monitor the level of DA using Ag nanoparticle (NP) dimers and enhanced Raman spectroscopy. METHODS: Ag NP dimers were synthesized for the sensitive detection of DA via surface-enhanced Raman scattering (SERS). Citrate was used as both the capping agent of NPs and sensing agent to DA, which is self-assembled on the surface of Ag NP dimers by reacting with the surface carboxyl group to form a stable amide bond. To improve accuracy and precision, the multiplicative effects model for surface-enhanced Raman spectroscopy was utilized to analyze the SERS assays. RESULTS: A low limits of detection (LOD) of 20 pM and a wide linear response range from 30 pM to 300 nM were obtained for DA quantitative detection. The SERS enhancement factor was theoretically valued at approximately 107 by discrete dipole approximation. DA was self-assembled on the citrate capped surface of Ag NPs dimers through the amide bond. The adsorption energy was estimated to be 256 KJ/mol using the Langmuir isotherm model. The density functional theory was used to simulate the spectral characteristics of SERS during the adsorption of DA on the surface of the Ag dimers. Furthermore, to improve the accuracy and precision of quantitative analysis of SERS assays with a multiplicative effects model for surface-enhanced Raman spectroscopy. CONCLUSION: A LOD of 20 pM DA-level was obtained, and the linear response ranged from 30 pM to 300 nM for quantitative DA detection. The absolute relative percentage error was 4.22% between the real and predicted DA concentrations. This detection scheme is expected to have good applications in the prevention and diagnosis of certain diseases caused by disorders in the DA level.

Using Fractional Intensities of Time-resolved Fluorescence to Sensitively Quantify NADH/NAD+ with Genetically Encoded Fluorescent Biosensors.

In this paper, we propose a novel and sensitive ratiometric analysis method that uses the fractional intensities of time-resolved fluorescence of genetically encoded fluorescent NADH/NAD+ biosensors, Peredox, SoNar, and Frex. When the conformations of the biosensors change upon NADH/NAD+ binding, the fractional intensities (α i τ i ) have opposite changing trends. Their ratios could be exploited to quantify NADH/NAD+ levels with a larger dynamic range and higher resolution versus commonly used fluorescence intensity and lifetime methods. Moreover, only one excitation and one emission wavelength are required for this ratiometric measurement. This eliminates problems of traditional excitation-ratiometric and emission-ratiometric methods. This method could be used to simplify the design and achieve highly sensitive analyte quantification of genetically encoded fluorescent biosensors. Wide potential applications could be developed for imaging live cell metabolism based on this new method.

Numerical Study of Novel Ratiometric Sensors Based on Plasmon-Exciton Coupling.

We numerically studied the optical properties of spherical nanostructures made of an emitter core coated by a silver shell through the generalized Mie theory. When there is a strong coupling between the localized surface plasmon in the metallic shell and the emitter exciton in the core, the extinction spectra exhibit two peaks. Upon adsorption of analytes on these core-shell nanostructures, the intensities of the two peaks change with opposite trends. This property makes them potential sensitive ratiometric sensors. Molecule adsorption on these nanostructures can be quantified through a very simple optical configuration likely resulting in a much faster acquisition time compared with systems based on the traditional metal nanoparticle surface plasmon resonance (SPR) biosensors.

[Fluorescence Properties of Single-Trp Peptide: Response to pH and Metal Ions].

Considering the important role of metal ions including copper ions are playing in human body, a novel single-Trp peptide WDAHSS was designed and synthesized in this study to achieve sensitive detection of copper ions via fluorescence spectroscopy. The intrinsic fluorescence of a tryptophan residue in WDAHSS, which was the only source of the molecular fluorescence, could be easily quenched with copper ions. By comparing fluorescence spectra of WDAHSS with those of tryptophan molecules at different pH values, the quenching mechanism of WDAHSS was explored in detail. Research showed that the histidine in WDAHSS bound copper ions with metal coordination. With participation of peptide bond, a square planar structure was formed. It was a consequent chelation of copper ions that caused the quenching of tryptophan residue. At the same time, this study discussed how pH conditions affected the fluorescence spectra of WDAHSS. Furthermore, association constants of copper ions towards WDAHSS were calculated through fluorescence measurements and fitting analyses. To enhance the anti-jamming ability to pH variation, the amino terminal of WDAHSS was intentionally acetylized, leading to a stable fluorescence emission under physiological pH conditions. Besides, WDAHSS was designed as a special structure to enhance the selectivity and biocompatibility of its sensitive detection of copper ions. Further studies on WDAHSS may help to improve the fluorescence imaging detection in vivo.

Sensitive Detection of Polycyclic Aromatic Molecules: Surface Enhanced Raman Scattering via π-π Stacking.

We report silver nanoparticles (Ag NPs) with high stability, sensitivity, and no surface enhanced Raman scattering (SERS) background. The Ag NPs were synthesized via a one-step process with polysodium styrenesulfonate (PSSS) templates, and they could efficiently adsorb polycyclic aromatic molecules via π-π stacking. The adsorption mechanisms and applicability were systematically studied by experimental measurements and theoretical simulations. When the polycyclic aromatic analytes were adsorbed on the PSSS-templated Ag NPs, the vibrations of π-π stacking-bound moieties were attenuated, yet those of the other unbound aromatic moieties increased. Most importantly, when the analytes had more than two π-π stacking binding sites, the PSSS-templated Ag NPs could trap the analytes by focusing through the optical force induced or via the simultaneously formed analyte-Ag NPs aggregates. This afforded high SERS intensity and very low detection limits.