Silver nanocube coupling with a nanoporous silver film for dual-molecule recognition based ultrasensitive SERS detection of dopamine

Surface-Enhanced Raman Scattering Nanosensing and Imaging in Neuroscience

Monitoring neurochemicals and imaging the molecular content of brain tissues in vitro, ex vivo, and in vivo is essential for enhancing our understanding of neurochemistry and the causes of brain disorders. This review explores the potential applications of surface-enhanced Raman scattering (SERS) nanosensors in neurosciences, where their adoption could lead to significant progress in the field. These applications encompass detecting neurotransmitters or brain disorders biomarkers in biofluids with SERS nanosensors, and imaging normal and pathological brain tissues with SERS labeling. Specific studies highlighting in vitro, ex vivo, and in vivo analysis of brain disorders using fit-for-purpose SERS nanosensors will be detailed, with an emphasis on the ability of SERS to detect clinically pertinent levels of neurochemicals. Recent advancements in designing SERS-active nanomaterials, improving experimentation in biofluids, and increasing the usage of machine learning for interpreting SERS spectra will also be discussed. Furthermore, we will address the tagging of tissues presenting pathologies with nanoparticles for SERS imaging, a burgeoning domain of neuroscience that has been demonstrated to be effective in guiding tumor removal during brain surgery. The review also explores future research applications for SERS nanosensors in neuroscience, including monitoring neurochemistry in vivo with greater penetration using surface-enhanced spatially offset Raman scattering (SESORS), near-infrared lasers, and 2-photon techniques. The article concludes by discussing the potential of SERS for investigating the effectiveness of therapies for brain disorders and for integrating conventional neurochemistry techniques with SERS sensing.

Breaking Barriers: Exploring Neurotransmitters through In Vivo vs. In Vitro Rivalry

Neurotransmitter analysis plays a pivotal role in diagnosing and managing neurodegenerative diseases, often characterized by disturbances in neurotransmitter systems. However, prevailing methods for quantifying neurotransmitters involve invasive procedures or require bulky imaging equipment, therefore restricting accessibility and posing potential risks to patients. The innovation of compact, in vivo instruments for neurotransmission analysis holds the potential to reshape disease management. This innovation can facilitate non-invasive and uninterrupted monitoring of neurotransmitter levels and their activity. Recent strides in microfabrication have led to the emergence of diminutive instruments that also find applicability in in vitro investigations. By harnessing the synergistic potential of microfluidics, micro-optics, and microelectronics, this nascent realm of research holds substantial promise. This review offers an overarching view of the current neurotransmitter sensing techniques, the advances towards in vitro microsensors tailored for monitoring neurotransmission, and the state-of-the-art fabrication techniques that can be used to fabricate those microsensors.

Aggregation of Ag nanoparticle based on surface acoustic wave for surface-enhanced Raman spectroscopy detection of dopamine

BACKGROUND

Dopamine (DA), a vital neurotransmitter, plays a critical role in the human brain and relates to neuropsychiatric disorders such as Parkinson's disease and schizophrenia. Numerous studies have explored detection of such biomarkers through surface-enhanced Raman spectroscopy (SERS). However, most of the studies focused on SERS detection face significant challenges with plasmonic nanostructure development. Such challenges often include time-consuming processes, complex fabrication, specialized chemical labeling, poor reproducibility, and random hotspot generation. Therefore, the need for simple and rapid nanostructure development is evident in SERS.

RESULTS

We propose an innovative SERS-active sensing technique for 50 nm silver nanoparticle (AgNP) clustering based on surface acoustic wave (SAW). When a 1 μL droplet of AgNP colloid is dispensed onto the SAW-propagation zone, the AgNP cluster is deposited after the droplet completely evaporates, developing plasmonic nanogaps for SERS hotspot caused by spherical AgNP aggregation. By optimizing the SAW system through the hydrophobic treatment and modulation of the operational power, the SAW-induced AgNP clustering showed densely packed AgNP within a dot-like configuration (∼2200 AgNP μm-2), effectively preventing particle welding. The characterization of 4-mercaptobenzoic acid as a probe analyte revealed that concentrations as low as 1.14 pM was detected using our SAW-SERS system under 785 nm laser excitation. Moreover, DA was detected up to 4.28 nM with a determination of 0.99 (R2).

SIGNIFICANCE

This technique for AgNP clustering induced by SAW provides a rapid, in situ, label-free SERS sensing method with outstanding sensitivity and linearity. A mere act of dropping can create extensive plasmonic hotspots featuring nanogap of ∼1.5 nm. The SAW-induced AgNP clustering can serve as an ultrasensitive SERS-active substrate for diverse molecular detections, including neurotransmitter detection.

Recent Advances in Catecholamines Analytical Detection Methods and Their Pretreatment Technologies

Catecholamines (CAs), including adrenaline, noradrenaline, and dopamine, are neurotransmitters and hormones that play a critical role in regulating the cardiovascular system, metabolism, and stress response in the human body. As promising methods for real-time monitoring of catecholamine neurotransmitters, LC-MS detectors have gained widespread acceptance and shown significant progress over the past few years. Other detection methods such as fluorescence detection, colorimetric assays, surface-enhanced Raman spectroscopy, and surface plasmon resonance spectroscopy have also been developed to varying degrees. In addition, efficient pretreatment technology for CAs is flourishing due to the increasing development of many highly selective and recoverable materials. There are a few articles that provide an overview of electrochemical detection and efficient enrichment, but a comprehensive summary focusing on analytical detection technology is lacking. Thus, this review provides a comprehensive summary of recent analytical detection technology research on CAs published between 2017 and 2022. The advantages and limitations of relevant methods including efficient pretreatment technologies for biological matrices and analytical methods used in combination with pretreatment technology have been discussed. Overall, this review article provides a better understanding of the importance of accurate CAs measurement and offers perspectives on the development of novel methods for disease diagnosis and research in this field.

Sericin-Based Bio-Inspired Nano-Engineering of Heterometallic AgAu Nanocubes for Attomolar Mefenamic Acid Sensing in the Mobile Phone-Based Surface Plasmon-Coupled Interface

Engineering photo-plasmonic platforms with heterometallic nanohybrids are of paramount significance for realizing augmented sensitivity in fluorescence-based analytical detection. Although myriad nanomaterials with versatile functionalities have been explored in this regard in the surface plasmon-coupled emission (SPCE) interface, light harvesting using nano-antennas synthesized via sustainable bio-inspired routes still remains a high priority in current research. Our study provides a rational design for in situ fabrication of nanoparticles of silver, gold, and their plasmonic hybrids using biocompatible, non-hazardous sericin protein (obtained Bombyx mori) as the reducing and capping agent. The one-pot, user-eco-friendly technology demonstrated here utilizes UV irradiation to promote the photo-induced electron transfer mechanism, thereby yielding nanomaterials of tunable optoelectronic functionalities. The resulting homometallic and heterometallic nanohybrids with robust localized surface plasmon resonances (LSPR) showed strong light-confining attributes when interfaced with the propagating surface plasmon polaritons (SPPs) of the SPCE platform, thereby yielding tunable, highly directional, polarized, and amplified fluorescence emission. The experimentally obtained emission profiles displayed an excellent correlation with the theoretically obtained dispersion diagrams validating the spectro-plasmonic results. The abundant hotspots from AgAu nanocubes presented in excess of 1300-fold dequenched fluorescence enhancement and were utilized for cost-effective and real-time mobile phone-based sensing of biologically relevant mefenamic acid at an attomolar limit of detection. We believe that this superior biosensing performance accomplished using the frugal bioinspired nano-engineering at hybrid interfaces would open new doors for developing nanofabrication protocols with the quintessential awareness of the principles of green nanotechnology, consequently eliminating hazardous chemicals and solvents in the development of point-of-care diagnostic tools.

Influence of the Co-Adsorbed Ions on the Surface-Enhanced Raman Scattering Spectra of Dopamine Adsorbed on Nanostructured Silver

The abnormal metabolism or imbalance of dopamine may lead to some neurological disorders. Therefore, the facile and fast detection of this neurotransmitter is essential in the early diagnosis of some diseases. One of the methods that can be used for the detection and determination of dopamine is the surface-enhanced Raman scattering (SERS). In this contribution, we report a very strong influence of some salts (we used salts containing Na⁺ cations and the following anions: SO₄^2-, F^-, Cl^-, Br^-, and I^-) on the spectral patterns and intensity of the SERS spectra of dopamine adsorbed on a nanostructured macroscopic silver substrate. The analysis of the recorded SERS spectra based on the assignments of Raman bands from the density-functional theory (DFT) calculations and based on the SERS surface selection rules reveals that when molecules of dopamine are adsorbed from an aqueous solution to which no electrolytes have been added, they adopt a flat orientation versus the silver surface; whereas, the molecules of dopamine co-adsorbed with various ions interact with the silver surface, mainly via phenolic groups, and they adopt a perpendicular orientation versus the metal surface. An addition of electrolytes also significantly influences the intensity of the recorded SERS spectrum; for example, an addition of Na₂SO₄ to a final concentration of 1 M induces an increase in the intensity of the measured SERS spectrum by a factor of ca. 40. This means that the addition of electrolytes to the analyzed solution can reduce the limit of detection of dopamine by SERS spectroscopy. The abovementioned findings may facilitate the construction of dopamine SERS sensors.

Study of the Fabrication of Gold Nanoparticle-Graphene-Arrayed Micro/Nanocavities as SERS Substrates Compared to Two Different Angles of Triangular Pyramid Tips

Surface-enhanced Raman scattering (SERS) has attracted attention because of its enormous potential to detect molecules with low concentrations. The method of fabricating SERS substrates is of great importance for improving the detection resolution. However, SERS substrates with different triangular pyramid tips fabricated by using the tip-based nanoindentation method has not been reported. Here, we prepared arrayed micro/nanocavities on copper-based graphene using the continuous indentation method with a Berkovich tip and a cube-corner tip, which have different face angles. Gold nanoparticles were then sputtered onto the graphene-copper micro/nanocavities to form the Au@GR@Cu micro/nanocavities SERS substrates. The substrates formed using the Berkovich tip and cube-corner tip were labeled B2-B9 and C2-C9, respectively, in which the numbers indicate the machining feed. Rhodamine 6G (R6G) was employed, and the Raman intensities of R6G on the differently arrayed Au@GR@Cu micro/nanocavities were measured. The Raman intensities of R6G were stronger on the pile-ups than on the inverted triangular pyramid cavities. The Raman intensities of R6G were highest on the C2 and B2 structures and lowest on the C9 and B9 structures. The Raman intensities of R6G on the arrayed Au@GR@Cu micro/nanocavities fabricated by the cube-corner tip were stronger than those on the arrayed Au@GR@Cu micro/nanocavities fabricated using the Berkovich tip with the same machining feed. In addition, the electric field intensity and distribution of the B9 and C9 arrayed Au@GR@Cu were simulated using Comsol software. Au@GR@Cu structures fabricated by the cube-corner tip were generated with higher electric field intensities. Furthermore, the relative standard deviations at 1362 cm^-1 of R6G were 6.19 and 6.62% on the C2 and C4 surfaces, respectively, showing good homogeneity. The SERS spectra of 10^-9 mol/L malachite green solution and 10^-6 mol/L carbaryl solution were recognized on the C1, C2, and C4 surfaces on day 1 and after 3 months, respectively. After storage at room temperature for 3 months, the reductions in the Raman intensities were less than 10%, indicating excellent stability. The results showed that the arrayed Au@GR@Cu micro/nanocavities fabricated using the cube-corner tip performed better than those fabricated using the Berkovich tip and exhibited excellent uniformity, availability, and stability, providing great potential for detecting pesticides at low concentrations.

Raman, Infrared and Brillouin Spectroscopies of Biofluids for Medical Diagnostics and for Detection of Biomarkers

This review surveys Infrared, Raman/SERS and Brillouin spectroscopies for medical diagnostics and detection of biomarkers in biofluids, that include urine, blood, saliva and other biofluids. These optical sensing techniques are non-contact, noninvasive and relatively rapid, accurate, label-free and affordable. However, those techniques still have to overcome some challenges to be widely adopted in routine clinical diagnostics. This review summarizes and provides insights on recent advancements in research within the field of vibrational spectroscopy for medical diagnostics and its use in detection of many health conditions such as kidney injury, cancers, cardiovascular and infectious diseases. The six comprehensive tables in the review and four tables in supplementary information summarize a few dozen experimental papers in terms of such analytical parameters as limit of detection, range, diagnostic sensitivity and specificity, and other figures of merits. Critical comparison between SERS and FTIR methods of analysis reveals that on average the reported sensitivity for biomarkers in biofluids for SERS vs FTIR is about 103 to 105 times higher, since LOD SERS are lower than LOD FTIR by about this factor. High sensitivity gives SERS an edge in detection of many biomarkers present in biofluids at low concentration (nM and sub nM), which can be particularly advantageous for example in early diagnostics of cancer or viral infections.HighlightsRaman, Infrared spectroscopies use low volume of biofluidic samples, little sample preparation, fast time of analysis and relatively inexpensive instrumentation.Applications of SERS may be a bit more complicated than applications of FTIR (e.g., limited shelf life for nanoparticles and substrates, etc.), but this can be generously compensated by much higher (by several order of magnitude) sensitivity in comparison to FTIR.High sensitivity makes SERS a noninvasive analytical method of choice for detection, quantification and diagnostics of many health conditions, metabolites, and drugs, particularly in diagnostics of cancer, including diagnostics of its early stages.FTIR, particularly ATR-FTIR can be a method of choice for efficient sensing of many biomarkers, present in urine, blood and other biofluids at sufficiently high concentrations (mM and even a few µM)Brillouin scattering spectroscopy detecting visco-elastic properties of probed liquid medium, may also find application in clinical analysis of some biofluids, such as cerebrospinal fluid and urine.

DNA Origami-Templated Bimetallic Nanostar Assemblies for Ultra-Sensitive Detection of Dopamine

The abundance of hotspots tuned via precise arrangement of coupled plasmonic nanostructures highly boost the surface-enhanced Raman scattering (SERS) signal enhancements, expanding their potential applicability to a diverse range of applications. Herein, nanoscale assembly of Ag coated Au nanostars in dimer and trimer configurations with tunable nanogap was achieved using programmable DNA origami technique. The resulting assemblies were then utilized for SERS-based ultra-sensitive detection of an important neurotransmitter, dopamine. The trimer assemblies were able to detect dopamine with picomolar sensitivity, and the assembled dimer structures achieved SERS sensitivity as low as 1 fM with a limit of detection of 0.225 fM. Overall, such coupled nanoarchitectures with superior plasmon tunability are promising to explore new avenues in biomedical diagnostic applications.

A simple and reliable approach for the fabrication of nanoporous silver patterns for surface-enhanced Raman spectroscopy applications

The fabrication of plasmonic nanostructures with a reliable, low cost and easy approach has become a crucial and urgent challenge in many fields, including surface-enhanced Raman spectroscopy (SERS) based applications. In this frame, nanoporous metal films are quite attractive, due to their intrinsic large surface area and high density of metal nanogaps, acting as hot-spots for Raman signal enhancement. In this paper, we report a detailed study on the fabrication of nanoporous silver-based SERS substrates, obtained by the application of two successive treatments with an Inductively Coupled Plasma (ICP) system, using synthetic air and Ar as feeding gases. The obtained substrates exhibit a quite broad plasmonic response, covering the Vis–NIR range, and an enhancement factor reaching 6.5 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times\, 10^7$$\end{document}×107, estimated by using 4-mercaptobenzoic acid (4-MBA) as probe molecule at 532 nm. Moreover, the substrates exhibit a quite good spatial reproducibility on a centimeter scale, which assures a good signal stability for analytical measurements. Globally, the developed protocol is easy and cost effective, potentially usable also for mass production thanks to the remarkable inter-batches reproducibility. As such, it holds promise for its use in SERS-based sensing platforms for sensitive detection of targets molecules.

Reusable 3D silver superposed silica SERS substrate based on the Griess reaction for the ratiometric detection of nitrite

When nitrite is ingested and absorbed by the body, it can be converted into highly toxic nitrosamines (carcinogens, teratogens, and mutagens), posing health risks to the general population. Therefore, it calls for establishing a method for determination of nitrite. In this paper, the glass-SiO₂-Ag surface-enhanced Raman scattering (SERS) substrate with a large number of "hot spots" were prepared by two kinds of silane coupling agents. The SERS substrate had high sensitivity and repeatability. Silicon dioxide supported the silver nanoparticles (Ag NPs), which increased surface roughness of the substrate, generated a great quantity of hot spots and enhanced the SERS signal. In the SERS spectrum, the intensity ratio of the two characteristic peaks (1287 cm^-1 and 1076 cm^-1) had a good linear correlation with the logarithm of the concentration of nitrite, R² = 0.9652. The recoveries of 50 μM and 100 μM nitrite in three kinds of foods, three kinds of cosmetics and tap water were 90.9-105.3%.

A covalent organic polymer-TiO2/Ti3C2 heterostructure as nonenzymatic biosensor for voltammetric detection of dopamine and uric acid

Heterostructures have potential to blend the advantages of each material, even exhibiting the evolutionary performance due to synergistic effects. Herein, covalent organic polymers (NUF) are integrated with a TiO₂/Ti₃C₂T_x nanocomposite (TiO₂/TiCT) to form TiO₂/TiCT-NUF heterojunctions as an enlarged nonenzymatic biosensor for dopamine (DA) and uric acid (UA). Detection is performed by differential pulse voltammetry (DPV). The TiO₂/TiCT/NUF exhibits high sensing activity with low detection limits of 0.2 and 0.18 nM (S/N = 3) in the concentration ranges from 0.002 to 100 μM and 0.001 to 60 μM for simultaneous determination of DA and UA, respectively. In addition, the TiO₂/TiCT/NUF provides good selectivity and reproducibility for DA and UA detection in urine and serum samples with recoveries of 98.4 to 100.9%. The proposed heterojunctions manifest an intriguing potential as a candidate of an electrochemical sensor for sole and simultaneous detection of DA and UA.

Metal Nanoparticles-Enhanced Biosensors: Synthesis, Design and Applications in Fluorescence Enhancement and Surface-enhanced Raman Scattering

Metal nanoparticles (NP) that exhibit localized surface plasmon resonance play an important role in metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS). Among the optical biosensors, MEF and SERS stand out to be the most sensitive techniques to detect a wide range of analytes from ions, biomolecules to macromolecules and microorganisms. Particularly, anisotropic metal NPs with strongly enhanced electric field at their sharp corners/edges under a wide range of excitation wavelengths are highly suitable for developing the ultrasensitive plasmon-enhanced biosensors. In this review, we first highlight the reliable methods for the synthesis of anisotropic gold NPs and silver NPs in high yield, as well as their alloys and composites with good control of size and shape. It is followed by the discussion of different sensing mechanisms and recent advances in the MEF and SERS biosensor designs. This includes the review of surface functionalization, bioconjugation and (directed/self) assembly methods as well as the selection/screening of specific biorecognition elements such as aptamers or antibodies for the highly selective bio-detection. The right combinations of metal nanoparticles, biorecognition element and assay design will lead to the successful development of MEF and SERS biosensors targeting different analytes both in-vitro and in-vivo. Finally, the prospects and challenges of metal-enhanced biosensors for future nanomedicine in achieving ultrasensitive and fast medical diagnostics, high-throughput drug discovery as well as effective and reliable theranostic treatment are discussed.