Surfactant-free interfacial growth of graphdiyne hollow microspheres and the mechanistic origin of their SERS activity

Three-dimensional urchin-like K2Ti8O17 / Ag NPs composite as a SERS substrate for detecting folic acid and thiram

The three-dimensional (3D) semiconductor/noble metal composite substrates for surface-enhanced Raman scattering (SERS) have garnered increasing interest due to their excellent optical and chemical properties, as well as the capacity to trigger both electromagnetic mechanism (EM) and chemical mechanism (CM) simultaneously. In this work, a facile 3D urchin-like K2Ti8O17/Ag nanoparticles (Ag NPs) composite substrate is designed for multi-purpose SERS sensing. K2Ti8O17, as a dielectric medium, improves the electric field environment around Ag NPs, which is consistent with finite-different time domain (FDTD) results, and enhances the SERS performance of the K2Ti8O17/Ag composite substrate. Besides, the efficient "donor-bridge-acceptor" charge transfer mode, explored through energy level calculations and enhanced utilization of incident light, further strengthens the SERS performance. Results show that the prepared K2Ti8O17/Ag NPs substrate exhibits high detection sensitivity, with 10-11 and 10-12 M limits in detecting Methylene Blue (MB) and Crystal Violet (CV), and the enhancement factors (EFs) of 2.66 × 109 and 6.07 × 109, respectively. At the same time, the composite substrate also possesses good signal uniformity (RSD = 10.5 %) and promising photocatalytic ability. For practical applications, the prepared K2Ti8O17/Ag NPs substrate can detect folic acid of 10-7 M in the diluted serum environment and thiram of 10-8 M in lake water, respectively. The urchin-like K2Ti8O17/Ag NPs substrate expands the range of 3D semiconductor composite SERS substrates, which is expected to be used for biosensing and trace analysis of harmful substances.

PCA-assisted direct diagnosis of Aβ proteins for Alzheimer's disease using non-metallic SERS platform of graphitic carbon nitride@metal-organic framework

Here, we explored a non-metallic surface enhanced Raman scattering (SERS) platform based on graphitic carbon nitride@metal-organic framework (g-C3N4@MOF) for the sensitive direct diagnosis of Aβ proteins, assisted by principal component analysis (PCA). By systematically optimizing the deposition voltage and time, we successfully achieved a uniform coating of g-C3N4 nanosheets over a large-area copper foil during the initial electrodeposition step. Subsequently, a homogeneous layer of flower-like MOF structures was deposited onto the g-C3N4 nanosheets through a secondary electrodeposition process. This cooperation of g-C3N4 nanosheets and flower-like MOF not only significantly enlarged the effective area for molecular enrichment but also promoted charge transfer through energy-level matching between the two materials. The characteristic SERS spectra of Aβ40 and Aβ42, enhanced by the g-C3N4@MOF composite substrate, were recorded and classified using PCA to extract informative features of these important biomarkers. This research exploits a new avenue for the clinical assay of neurodegenerative diseases by extracting informative features of key biomarkers.

A local shrinkage approach for creating dynamic hot-spots on thermoresponsive nanocellulose-based SERS substrate

Surface-enhanced Raman scattering (SERS) is a highly sensitive technology to detect target analytes. The construction of dynamic "hot-spots" represents a significant approach to enhancing detection sensitivity. Herein, a hybrid plasma platform with dynamic "hot-spots" was developed for SERS recognition based on the assembly of gold nanospheres (AuNSs) on temperature-sensitive bacterial cellulose (BC) film grafted with poly(N-isopropylacrylamide) (PNIPAM). The dynamic "hot-spots" structure was regulated in-situ by local conformational contraction of the grafted thermoresponsive PNIPAM around the BC backbone without changing the overall morphology of the substrate. Moreover, the heating process was simplified by utilizing the plasma photothermal effect of AuNSs to regulate the "hot-spot" structure. The dynamic regulation measured value of the Raman signal of Rhodamine 6G (R6G) was increased by 6.5-times, and the SERS substrate exhibited extremely high sensitivity with a limit of detection (LOD) of 8.47 × 10-9 g/L and a relative standard deviation (RSD) of 9.24 %. Meanwhile, it can accurately detect the pesticide residues of thiram on apple peel with the detection limit of 6.54 × 10-11 g/L. This dynamic "hot-spot" modulation strategy via local structural regulation has significant potential to improve the convenience, flexibility, and sensitivity of on-site SERS detection.

Modulating the electronic structure of graphdiyne-based nanomaterials for engineering nano-bio interfaces in biomedical applications

Graphdiyne (GDY), a two-dimensional (2D) carbon allotrope featuring a unique electronic structure, has attracted considerable attention due to its outstanding properties and potential applications in various fields, particularly in biomedicine due to its exceptional surface area, tunable electronic structure, and biocompatibility. Although promising, this field is still in the proof-of-concept stage due to incomplete understanding of the effects of structural regulation, particularly electronic structure, of GDY-based nanomaterials on their nano-bio interfaces, which seriously hinders the research of GDY-based nanomaterials in the biomedical field. To provide a comprehensive understanding of the relationship between electronic structures and nano-bio interfaces, this review focuses on the modulation of the electronic structure of GDY-based nanomaterials and its implications for engineering nano-bio interfaces for biomedical applications. Firstly, we delve into the intrinsic electronic properties of GDY, including its bandgap tunability and high carrier mobility, which are critical for its functionality in biomedical applications. We then discuss strategies for modulating these properties through oxidation, nonmetallic doping, covalent modification, and metal loading, aiming to optimize the electronic structure of GDY-based nanomaterials for superior performance in specific biomedical contexts, such as biomedical imaging, surface and interface catalysis, free radical scavenging, and drug delivery. Furthermore, we provide an overview of the methodologies for the investigation of these electronic properties, including theoretical simulation, characterization techniques, and real-time analysis of electron transfer at the nano-bio interfaces, highlighting their roles in advancing our understanding and guiding the design of novel GDY-based materials. Finally, this review provides an outlook on future research directions aimed at further optimizing the design of GDY-based nanomaterials and nano-bio interfaces, emphasizing the need for interdisciplinary collaboration to overcome current challenges and to fully realize the potential of GDY-based nanomaterials in biomedical applications. These principles are anticipated to facilitate the future development and clinical translation of precise, safe, and effective nanomedicines with intelligent theranostic features.

Insights of Surface-Enhanced Raman Spectroscopy Detection by Guiding Molecules into Nanostructures to Activate Hot Spots

A misunderstanding of how target molecules enter hot spot nanostructures has significantly hindered the advancement of surface-enhanced Raman spectroscopy (SERS) detection methods in recent years. The challenge lies in finding convenient ways to transport target molecules to various nanostructures. In this work, we discovered that filling the gaps in empty nanostructures with water is often difficult, as metal surfaces are not well wetted. Additionally, the adsorption of pollutants from the air reduces the water wettability within the nanogaps, severely restricting the diffusion of molecules in the hot spots. This study proposes a method that uses a binary solvent mixture of ethanol and water (EtOH-H2O) to effectively guide target molecules into the nanostructures containing numerous hot spots. By utilizing the tunable surface tension gradient of this binary solvent mixture, we can control solvent transport within the nanostructures, significantly enhancing the activity of the hot spots and increasing the efficiency of SERS detection. The detection limit of this simple and rapid binary solvent mixing method is improved by 2-3 orders of magnitude compared to traditional methods that use only water or ethanol as solvents while also demonstrating high reproducibility. This method can be widely applied to various nanostructures for different types of molecules, maximizing the efficient use of intrinsic hot spots. This innovative approach provides new momentum for the advancement of SERS technology and lays a solid foundation for its widespread adoption in various analytical applications.

Femtosecond laser-induced Au nanostructure-decorated with plasmonic nanomaterials for sensitive SERS-based detection of fentanyl

Fentanyl and its analogs have emerged as the main factor behind the ongoing opioid abuse globally in recent years. However, the existing techniques for sensitive and accurate detection of fentanyl are often complex, laborious, expensive, and restricted to central healthcare facilities. We reported herein a plasmonic biochip fabricated by the femtosecond laser-induced nanostructures and plasmonic nanomaterials for sensitive SERS-based detection of fentanyl. Yolk-shell structured plasmonic nanomaterials are employed owing to their unique optical properties. The femtosecond laser direct writing technique creates three-dimensional silicon nanostructures followed by gold deposition and the immobilization of plasmonic nanomaterials. This SERS biochip fabricated by the femtosecond laser-induced nanostructure decorated with yolk-shell structured plasmonic nanomaterials enables the rapid and sensitive detection of fentanyl with the limit of detection of 3.33 ng/mL.

Three-Dimensional SERS-Active Hydrogel Microbeads Enable Highly Sensitive Homogeneous Phase Detection of Alkaline Phosphatase in Biosystems

Alkaline phosphatase (ALP) is a biomarker for many diseases, and monitoring its activity level is important for disease diagnosis and treatment. In this study, we used the microdroplet technology combined with an in situ laser-induced polymerization method to prepare the Ag nanoparticle (AgNP) doped hydrogel microbeads (HMBs) with adjustable pore sizes that allow small molecules to enter while blocking large molecules. The AgNPs embedded in the hydrogel microspheres can provide SERS activity, improving the SERS signal of small molecules that diffuse to the AgNPs. A specific hydrolysis reaction of ALP on 5-bromo-4-chloro-3-indolylphosphate (BCIP) was introduced and itsproduct 5,5'-dibromo-4,4'-dichloro-1H,1H-[2,2']bisindolyl-3,3'-dione (BCI) was employed to assess ALP activity due to its highly resonance Raman activity. The sensing platform was applied to model ALP activity in serum and evaluate ALP inhibitors. The SERS assay showed higher sensitivity than UV-vis absorption spectroscopy, with the lowest detectable ALP concentration of 1.0 × 10-20 M. In addition, the ALP activity in HepG2 cells was evaluated using this sensing platform, showing lower ALP-expressing activity than that of controls in response to hypoxia and iron metastasis. This SERS-activated HMB shows great potential in detecting ALP and is expected to help analyze complex clinical samples.

The Interfacial Interpenetration Effect for Controlled Reaction Stability of Palladium Catalysts

Tailoring well-defined interfacial structures of heterogeneous metal catalysts has become an effective strategy for identifying the interface relationships and facilitating the reactions involving multiple intermediates. Here, a particle-particle heterostructure catalyst consisting of Pd and copper oxide nanoparticles is designed to achieve high-performance alkaline methanol oxidation electrocatalysis. The strong coupling particle-particle heterostructure catalyst induced a unique interfacial interpenetration effect to improve the interfacial charge redistribution and regulate the d-band structure for optimizing the adsorption of CO intermediates on the catalyst. The resulting catalyst shows impressive mass activity (4.0 A mgPd-1) and current density (215.8 mA cm-2) for the methanol oxidation reaction (MOR) in alkaline media, which is 80.0 and 154.1 times higher than 10% Pd/C. The catalyst also exhibited outstanding stability for the MOR without obvious mass activity decay after 30,000 cycles. Experimental results and theoretical simulation (DFT) studies show that the chemical bond of the Cu-O-Pd interface can be regulated by the Pd penetration effect, greatly improving the activity and stability of the MOR. The present work exhibits the superiority of the metal particle-metal oxide heterostructure interface toward the rational design of advanced electrocatalysts.

High-specificity SERS sensing with magnet-powered hierarchically structured micromotors

This work reports a hierarchically structured micromotor (HSM) surface-enhanced Raman scattering (SERS) platform comprising 3D tubular configurations with nanostructured outer walls. The HSMs can be powered by an external magnetic field in solution to enrich molecules with promoted adsorption efficiency. The nanostructured outer wall serves as containers to collect molecules and produce strong localized surface plasmon resonance to intensify Raman of the enriched molecules. Further coupling of HSMs after molecular enrichment can produce additional plasmonic hotspots at the sites where the molecules were enriched, providing a solution to manipulate molecules to enter the plasmonic hotspot region. Moreover, functionalizing specific molecules on the outer wall of HSMs enables high-specificity SERS sensing for benzaldehyde (BA) and Cu2+ ions in liquid. This SERS platform demonstrates great potential for practical applications in biochemical analysis and environmental monitoring, offering a rapid and sensitive tool for detecting low-concentration analytes in liquid.

A flexible plasmonic substrate for sensitive surface-enhanced Raman scattering-based detection of fentanyl

In this work, we demonstrate a straightforward and versatile approach for fabricating flexible SERS substrates for highly sensitive fentanyl detection. Our design strategy integrates the synthesis of a yolk-shell structured plasmonic nanomaterial with a flexible cellulose substrate. The resulting SERS platform demonstrates excellent sensing capabilities, achieving a fentanyl detection limit as low as 4.89 ng mL-1.

Nitrogen-doped graphene quantum dot-intensified tungsten oxide nanosheets as a SERS substrate for antibiotics detection

In this study, tungsten oxide nanosheets loaded with nitrogen-doped graphene oxide quantum dots (NGQDs/WO3 NSs) were fabricated as SERS substrates. The promoted photo-induced charge transfer (PICT) and the strong π-π stacking effect resulting from the unique structure of the NGQDs contributed to the enhanced SERS signal.

Phase Transformation on Two-Dimensional MoTe2 Films for Surface-Enhanced Raman Spectroscopy

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy (SERS) owing to their atomically flat surfaces and adjustable electronic properties. Herein, large-scale 2D 1T'- and 2H-MoTe2 films were prepared using a chemical vapor deposition method. We found that phase structure plays an important role in the enhancement of the SERS performances of MoTe2 films. 1T'-MoTe2 films showed a strong SERS effect with a detection limit of 1 × 10-9 M for the R6G molecule, which is one order of magnitude lower than that of 2H-MoTe2 films. We demonstrated that the SERS sensitivity of MoTe2 films is derived from the efficient photoinduced charge transfer process between MoTe2 and adsorbed molecules. Moreover, a prohibited fish drug could be detected by using 1T'-MoTe2 films as SERS substrates. Our study paves the way to the development and application of high-performance SERS substrates based on TMD phase engineering.

Cu/CuxO/Graphdiyne Tandem Catalyst for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrocatalytic reduction reaction of nitrate (NO3 -) to ammonia (NH3) is a feasible way to achieve artificial nitrogen cycle. However, the low yield rate and poor selectivity toward NH3 product is a technical challenge. Here a graphdiyne (GDY)-based tandem catalyst featuring Cu/CuxO nanoparticles anchored to GDY support (termed Cu/CuxO/GDY) for efficient electrocatalytic NO3 - reduction is presented. A high NH3 yield rate of 25.4 mg h-1 mgcat. -1 (25.4 mg h-1 cm-2) with a Faradaic efficiency of 99.8% at an applied potential of -0.8 V versus RHE using the designed catalyst is achieved. These performance metrics outperform most reported NO3 - to NH3 catalysts in the alkaline media. Electrochemical measurements and density functional theory reveal that the NO3 - preferentially attacks Cu/CuxO, and the GDY can effectively catalyze the reduction of NO2 - to NH3. This work highlights the efficacy of GDY as a new class of tandem catalysts for the artificial nitrogen cycle and provides powerful guidelines for the design of tandem electrocatalysts.

Dual-mode SERS/colorimetric sensing of nitrite in meat products based on multifunctional au NPs@COF composite

The presence of nitrite in food products has generated significant public concern. A simple and rapid dual-mode surface-enhanced Raman spectroscopy (SERS)/colorimetric detection of nitrite is proposed based on a diazo reaction and multifunctional gold nanoparticle-doped covalent organic framework (Au@COF) composite. Under acidic conditions, the reaction between toluidine blue and nitrite yielded a colorless diazo salt, simultaneously attenuating its characteristic absorption peak and Raman signal. The multifunctional Au@COF materials enhanced the Raman signal and ensured good reproducibility. Additionally, the reaction rates improved, and the sensitivity was enhanced due to the excellent adsorption capacity of the COF. The proposed method demonstrated high sensitivity and excellent recovery rates for nitrite detection in food samples. This approach shows potential for precisely detecting nitrite content in real-world food samples by integrating the simplicity of colorimetric analysis with the enhanced sensitivity of SERS.

Development and Biomedical Application of Non-Noble Metal Nanomaterials in SERS

Surface-enhanced Raman scattering (SERS) is vital in many fields because of its high sensitivity, fast response, and fingerprint effect. The surface-enhanced Raman mechanisms are generally electromagnetic enhancement (EM), which is mainly based on noble metals (Au, Ag, etc.), and chemical enhancement (CM). With more and more studies on CM mechanism in recent years, non-noble metal nanomaterial SERS substrates gradually became widely researched and applied due to their superior economy, stability, selectivity, and biocompatibility compared to noble metal. In addition, non-noble metal substrates also provide an ideal new platform for SERS technology to probe the mechanism of biomolecules. In this paper, we review the applications of non-noble metal nanomaterials in SERS detection for biomedical engineering in recent years. Firstly, we introduce the development of some more common non-noble metal SERS substrates and discuss their properties and enhancement mechanisms. Subsequently, we focus on the progress of the application of SERS detection of non-noble metal nanomaterials, such as analysis of biomarkers and the detection of some contaminants. Finally, we look forward to the future research process of non-noble metal substrate nanomaterials for biomedicine, which may draw more attention to the biosensor applications of non-noble metal nanomaterial-based SERS substrates.

Growing highly ordered Pt and Mn bimetallic single atomic layers over graphdiyne

Controlling the precise growth of atoms is necessary to achieve manipulation of atomic composition and atomic position, regulation of electronic structure, and an understanding of reactions at the atomic level. Herein, we report a facile method for ordered anchoring of zero-valent platinum and manganese atoms with single-atom thickness on graphdiyne under mild conditions. Due to strong and incomplete charge transfer between graphdiyne and metal atoms, the formation of metal clusters and nanoparticles can be inhibited. The size, composition and structure of the bimetallic nanoplates are precisely controlled by the natural structure-limiting effect of graphdiyne. Experimental characterization clearly demonstrates such a fine control process. Electrochemical measurements show that the active site of platinum-manganese interface on graphdiyne guarantees the high catalytic activity and selectivity (~100%) for alkene-to-diol conversion. This work lays a solid foundation for obtaining high-performance nanomaterials by the atomic engineering of active site.

Graphdiyne Enabled Nitrogen Vacancy Formation in Copper Nitride for Efficient Ammonia Synthesis

The electrocatalytic reduction of nitrate is promising for sustainable ammonia synthesis but suffers from slow reduction kinetics and multiple competing reactions. Here, we report a catalyst featuring copper nitride (Cu3N) anchored on a novel graphdiyne support (termed Cu3N/GDY), which is used for electrocatalytic reduction of nitrate to produce ammonia. The GDY absorbed hydrogen and enabled nitrogen (N) vacancy formation in Cu3N for the fast nitrate reduction reaction (NO3RR). Further, the distinct absorption sites formed by GDY and N vacancy enabled the excellent selectivity and stability of NO3RR. Notably, the Cu3N/GDY catalyst achieved a high ammonia yield (YNH3) up to 35280 μg h-1 mgcat.-1 and a high Faradaic efficiency (FE) of 98.1% using 0.1 M NO3- at -0.9 V versus a reversible hydrogen electrode (RHE). Using electron paramagnetic resonance (EPR) technology and in situ X-ray absorption fine structure (XAFS) spectroscopy measurement, we visualized the N vacancy formation in Cu3N and electrocatalytic NO3RR enabled by GDY. These findings show the promise of GDY in sustainable ammonia synthesis and highlight the efficacy of Cu3N/GDY as a catalyst.

Harnessing Graphdiyne for Selective Cu2+ Detection: A Promising Tool for Parkinson's Disease Diagnostics and Pathogenesis

Cu2+ accelerates the viral-like propagation of α-synuclein fibrils and plays a key role in the pathogenesis of Parkinson's disease (PD). Therefore, the accurate detection of Cu2+ is essential for the diagnosis of PD and other neurological diseases. The Cu2+ detection process is impeded by substances that have similar electrochemical properties. In this study, graphdiyne (GDY), a new kind of carbon allotrope with strong electron-donating ability, was utilized for the highly selective detection of Cu2+ by taking advantage of its outstanding adsorption capacity for Cu2+. Density functional theory (DFT) calculations show that Cu atoms are adsorbed in the cavity of GDY, and the absorption energy between Cu and C atoms is higher than that of graphene (GR), indicating that the cavity of GDY is favorable for the adsorption of Cu atoms and electrochemical sensing. The GDY-based electrochemical sensor can effectively avoid the interference of amino acids, metal ions and neurotransmitters and has a high sensitivity of 9.77 μA·μM-1·cm-2, with a minimum detectable concentration of 200 nM. During the investigating pathogenesis and therapeutic process of PD with α-synuclein as the diagnostic standard, the concentration of Cu2+ in cells before and after L-DOPA and GSH treatments were examined, and it was found that Cu2+ exhibits high potential as a biomarker for PD. This study not only harnesses the favorable adsorption of the GDY and Cu2+ to improve the specificity of ion detection but also provide clues for deeper understanding of the role of Cu2+ in neurobiology and neurological diseases.

Microfluidics-aided fabrication of 3D micro-nano hierarchical SERS substrate for rapid detection of dual hepatocellular carcinoma biomarkers

The simultaneous analysis of trace amounts of dual biomarkers is crucial in the early diagnosis, treatment, and prognosis of hepatocellular carcinoma (HCC). In this study, we prepared SERS-active hydrogel microparticles (SAHMs) with 3D hierarchical gold nanoparticles (AuNPs) micro-nanostructures by microdroplet technology and in situ synthesis, which demonstrated high reproducibility and sensitivity. Compared with traditional 2D SERS substrates, this newly prepared 3D SERS substrate provided a high density of nano-wrinkled structures and numerous AuNPs. Furthermore, a newly designed SERS-active substrate was proposed for the simultaneous microfluidic detection of AFP and AFU. The Raman signals of sandwich immunocomplexes on the surface of the SAHMs were measured for the trace analysis of these biomarkers. The proposed microfluidic platform achieved AFP and AFU detection in the range of 0.1-100 ng mL-1 and 0.01-100 ng mL-1, respectively, which represents a good response. Indeed, this platform is easy to fabricate, of low cost and has short detection time and comparable detection limits to other methods. As far as we know, this is the first study to achieve the simultaneous detection of AFP and AFU on a microfluidic platform. Therefore, we proposed a new simultaneous detection platform for dual HCC biomarkers that shows strong potential for the early diagnosis of HCC.