Surface-enhanced Raman Scattering Nanoprobes Research Articles

NIR‐II Surface‐Enhanced Raman Scattering Nanoprobes in Biomedicine: Current Impact and Future Directions

AbstractThe field of second near‐infrared (NIR‐II) surface‐enhanced Raman scattering (SERS) nanoprobes has made commendable progress in biomedicine. This article reviews recent advances and future development of NIR‐II SERS nanoprobes. It introduces the fundamental principles of SERS nanoprobes and highlights key advances in the NIR‐II window, including reduced tissue attenuation, deep penetration, maximized allowable exposure, and improved photostability. The discussion of future directions includes the refinement of nanoprobe substrates, emphasizing the tailoring of optical properties of metallic SERS‐active nanoprobes, and exploring non‐metallic alternatives. The intricacies of designing Raman reporters for the NIR‐II resonance and the potential of these reporters to advance the field are also discussed. The integration of artificial intelligence (AI) into nanoprobe design represents a cutting‐edge approach to overcome current challenges. This article also examines the emergence of deep Raman techniques for through‐tissue SERS detection, toward NIR‐II SERS tomography. It acknowledges instrumental advancements like improved charge‐coupled device sensitivity and accelerated imaging speeds. The article concludes by addressing the critical aspects of biosafety, ease of functionalization, compatibility, and the path to clinical translation. With a comprehensive overview of current achievements and future prospects, this review aims to illuminate the path for NIR‐II SERS nanoprobes to innovate diagnostic and therapeutic approaches in biomedicine.

Design and Synthesis of SERS Materials for In Vivo Molecular Imaging and Biosensing.

Surface-enhanced Raman scattering (SERS) is a feasible and ultra-sensitive method for biomedical imaging and disease diagnosis. SERS is widely applied to in vivo imaging due to the development of functional nanoparticles encoded by Raman active molecules (SERS nanoprobes) and improvements in instruments. Herein, the recent developments in SERS active materials and their in vivo imaging and biosensing applications are overviewed. Various SERS substrates that have been successfully used for in vivo imaging are described. Then, the applications of SERS imaging in cancer detection and in vivo intraoperative guidance are summarized. The role of highly sensitive SERS biosensors in guiding the detection and prevention of diseases is discussed in detail. Moreover, its role in the identification and resection of microtumors and as a diagnostic and therapeutic platform is also reviewed. Finally, the progress and challenges associated with SERS active materials, equipment, and clinical translation are described. The present evidence suggests that SERS could be applied in clinical practice in the future.

Ultrasensitive detection of SARS-CoV-2 S protein with aptamers biosensor based on surface-enhanced Raman scattering.

A rapid and accurate diagnostic modality is essential to prevent the spread of SARS-CoV-2. In this study, we proposed a SARS-CoV-2 detection sensor based on surface-enhanced Raman scattering (SERS) to achieve rapid and ultrasensitive detection. The sensor utilized spike protein deoxyribonucleic acid aptamers with strong affinity as the recognition entity to achieve high specificity. The spherical cocktail aptamers-gold nanoparticles (SCAP) SERS substrate was used as the base and Au nanoparticles modified with the Raman reporter molecule that resonates with the excitation light and spike protein aptamers were used as the SERS nanoprobe. The SCAP substrate and SERS nanoprobes were used to target and capture the SARS-CoV-2 S protein to form a sandwich structure on the Au film substrate, which can generate ultra-strong "hot spots" to achieve ultrasensitive detection. Analysis of SARS-CoV-2 S protein was performed by monitoring changes in SERS peak intensity on a SCAP SERS substrate-based detection platform. This assay detects S protein with a LOD of less than 0.7 fg mL-1 and pseudovirus as low as 0.8 TU mL-1 in about 12min. The results of the simulated oropharyngeal swab system in this study indicated the possibility of it being used for clinical detection, providing a potential option for rapid and accurate diagnosis and more effective control of SARS-CoV-2 transmission.

Internal Standard Assisted Surface-Enhanced Raman Scattering Nanoprobe with 4-NTP as Recognition Unit for Ratiometric Imaging Hydrogen Sulfide in Living Cells.

Hydrogen sulfide (H2S), as the third endogenous gasotransmitter, is closely associated with various physiological and pathological processes, whereas many aspects of its functions remain unclear. Effective tools for the accurate detection of H2S in living organisms are urgently needed. We herein reported an internal standard assisted surface-enhanced Raman scattering (SERS) nanoprobe for ratiometric detection of H2S in vitro and in living cells based on the reduction of nitros with H2S. This nanoprobe consists of an internal standard (4-mercaptobenzonitrile, MPBN) embedded core-molecule-shell Au nanoflower (Au@MPBN@Au) as the high plasmonic active SERS substrate and the 4-nitrothiophenol (4-NTP) molecule immobilized on the surface as the H2S recognition unit. With the addition of H2S, the nitros peak (1329 cm-1) decreased. Meanwhile, three obvious new peaks appeared at 1139, 1387, and 1433 cm-1, which were related to the vibration of the dimerized product 4,4'-dimercaptoazobisbenzene (DMAB) of 4-aminothiophenol (4-ATP). However, the peak intensity at 2223 cm-1 derived from MPBN was not influenced by the outer environment. Thus, the H2S level was able to be determined based on the ratio of two peak intensities (I1139/I2223) with a detection limit as low as 0.24 μM. Notably, we have proved that SERS nanoprobe Au@MPBN@Au@4-NTP could ratiometrically image both the endogenous and exogenous H2S in living cells. We anticipate that Au@MPBN@Au@4-NTP could be applied for the study of H2S-related physiological function in the future.

Rapid and sensitive detection of zearalenone in corn using SERS-based lateral flow immunosensor

Zearalenone (ZEN) is a universal mycotoxin contaminant in corn and its products. A surface-enhanced Raman scattering (SERS) based test strip was proposed for the detection of ZEN, which had the advantages of simplicity, rapidity, and high sensitivity. Core-shell Au@AgNPs with embedded reporter molecules (4-MBA) were synthesized as SERS nanoprobe, which exhibited excellent SERS signals and high stability. The detection range of ZEN for corn samples was 10–1000 μg/kg with the limit of detection (LOD) of 3.6 μg/kg, which is far below the recommended tolerable level (60 μg/kg). More importantly, the SERS method was verified by HPLC in the application on corn samples contaminated with ZEN, and the coincidence rates were in the range of 86.06%–111.23%, suggesting a high accuracy of the SERS assay. Therefore, the SERS-based test strip with an analysis time of less than 15 min is a promising tool for accurate and rapid detection of ZEN-field contamination.

Boosting the Brightness of Thiolated Surface-Enhanced Raman Scattering Nanoprobes by Maximal Utilization of the Three-Dimensional Volume of Electromagnetic Fields.

Self-assembled monolayers (SAMs) of thiols on plasmonic nanoparticles constitute one of the most common methods for fabricating surface-enhanced Raman scattering (SERS) nanoprobes with wide applications. However, this method greatly limits the sufficient utilization of electromagnetic fields derived from plasmon excitation of the nanoparticles, because the thickness of SAMs (<1 nm) is usually much smaller than the attenuation length (>10 nm) of the fields. To overcome this, we propose a three-dimensional (3D) volume-active SERS (VASERS) technique to break the SAM limit, which integrates large amounts of thiol reporters into polydopamine shells on silver nanoparticles via Michael addition and allows sufficient utilization of 3D electromagnetic fields, leading to a dramatic increase in the intensity of the signal of the nanoprobes by about one order of magnitude. We demonstrate the universality of this strategy on various thiol reporters and plasmonic substrates. We also show that orthogonal VASERS nanoprobes with alkyne readout allow for high-precision in vivo tumor targeting and margin delineation.

DNAzyme signal amplification based on Au@Ag core-shell nanorods for highly sensitive SERS sensing miRNA-21.

Here, we developed a surface-enhanced Raman scattering (SERS) sensor based on functionalized Au@Ag core-shell nanorods (Au@Ag NRs) and cascade DNAzyme amplifier (CSA) for sensitive and accurate determination of microRNA-21 (miRNA-21). The as-prepared SERS nanoprobes were composed of a thiol-modification hairpin probe (HP2)-functionalized Au@Ag NRs and hairpin DNAzyme (HP1-Dz). Compared with original gold nanorods, the silver shell caused an enhancement of plasmonic properties, resulting in a significant enhancement of Raman signals. In the presence of target miRNAs, the hairpin construction of HP1-Dz changed due to DNA/RNA hybridization; subsequently, the DNAzyme-catalyzed cleaving process changed, and the Raman signals of the SERS nanoprobes gradually "turned off" with time elapse because of the dissociation of the Raman reporter from the surface of Au@Ag NRs. Hence, based on this principle, the proposed SERS sensor exhibited good linearity in the range 0.5 fM to 10nM for miRNA-21 detection with a detection limit (LOD) of 0.5 fM. The proposed SERS platform has potential application in quantitative and precise detection of miRNA-21 in human serum.

Highly sensitive near-infrared SERS nanoprobes for in vivo imaging using gold-assembled silica nanoparticles with controllable nanogaps

BackgroundTo take advantages, such as multiplex capacity, non-photobleaching property, and high sensitivity, of surface-enhanced Raman scattering (SERS)-based in vivo imaging, development of highly enhanced SERS nanoprobes in near-infrared (NIR) region is needed. A well-controlled morphology and biocompatibility are essential features of NIR SERS nanoprobes. Gold (Au)-assembled nanostructures with controllable nanogaps with highly enhanced SERS signals within multiple hotspots could be a breakthrough.ResultsAu-assembled silica (SiO2) nanoparticles (NPs) (SiO2@Au@Au NPs) as NIR SERS nanoprobes are synthesized using the seed-mediated growth method. SiO2@Au@Au NPs using six different sizes of Au NPs (SiO2@Au@Au50–SiO2@Au@Au500) were prepared by controlling the concentration of Au precursor in the growth step. The nanogaps between Au NPs on the SiO2 surface could be controlled from 4.16 to 0.98 nm by adjusting the concentration of Au precursor (hence increasing Au NP sizes), which resulted in the formation of effective SERS hotspots. SiO2@Au@Au500 NPs with a 0.98-nm gap showed a high SERS enhancement factor of approximately 3.8 × 106 under 785-nm photoexcitation. SiO2@Au@Au500 nanoprobes showed detectable in vivo SERS signals at a concentration of 16 μg/mL in animal tissue specimen at a depth of 7 mm. SiO2@Au@Au500 NPs with 14 different Raman label compounds exhibited distinct SERS signals upon subcutaneous injection into nude mice.ConclusionsSiO2@Au@Au NPs showed high potential for in vivo applications as multiplex nanoprobes with high SERS sensitivity in the NIR region.Graphical

A Rational Designed Bioorthogonal Surface-Enhanced Raman Scattering Nanoprobe for Quantitatively Visualizing Endogenous Hydrogen Sulfide in Single Living Cells.

Understanding the biology of gasotransmitters in living cells is of significance but remains challenging due to largely a lack of robust molecular probes. Here, we present the facile design and synthesis of a bioorthogonal Raman probe, 4-azidobenzenethiol (4-ABT), for endogenous hydrogen sulfide (H2S) imaging in single live cells by surface-enhanced Raman scattering (SERS). 4-ABT bears a thiol group and an azido group in the benzene ring, thus affording a bifunction to firmly bind to the gold nanoparticle surface and specifically respond to H2S. Moreover, the 4-ABT-based SERS nanoprobe shows a dose-dependent spectral change in the cellular Raman-silent region upon reacting with H2S, allowing ratiometric quantitative detection and visualization of intracellular H2S status without bio-interference. The ease of fabrication and superior performance of the novel SERS nanoprobe demonstrate its promising application in studies of H2S-related signaling networks.

Design and evaluation of Raman reporters for the Raman-silent region.

Rationale: Surface enhanced Raman scattering (SERS) is proving to be a useful tool for biomedical imaging. However, this imaging technique can suffer from poor signal-to-noise ratio, as the complexity of biological tissues can lead to overlapping of Raman bands from tissues and the Raman reporter molecule utilized. Methods: Herein we describe the synthesis of triple bond containing Raman reporters that scatter light in the biological silent window, between 1750 cm-1 and 2750 cm-1. Results: Our SERS nanoprobes are comprised of uniquely designed Raman reporters containing either alkyne- or cyano-functional groups, enabling them to be readily distinguished from background biological tissue. Conclusion: We identify promising candidates that eventually can be moved forward as Raman reporters in SERS nanoparticles for highly specific contrast-enhanced Raman-based disease or analyte detection in biological applications.

Directional self-assembly of anisotropic bimetal-poly(aniline) nanostructures for rheumatoid arthritis diagnosis in multiplexing

Anisotropic organic-inorganic hybrid nanoparticles possessing different functionalities and physicochemical properties from each compartment have attracted significant interest for the development of advanced functional materials. Moreover, their self-assembled structures exhibit unique optical properties for photonics-based biosensing. We report herein the fabrication of anisotropic bimetal-polymer nanoparticles (ABPNs) via combination of oxidative polymerization and additional growth of metallic nanoparticles on Au seeds as well as their directional clustering mediated via noncovalent interactions. Polymerization of anilines for poly (aniline) shell was conducted by reducing silver nitrate onto the Au seed in the presence of a surfactant, giving rise to spatially distinct bimetallic Au core and Ag shell compartment and the poly (aniline) counter-one that comprise the ABPNs. Furthermore, ABPNs were directionally clustered in a controlled manner via hydrophobic interaction, when the bimetallic compartment was selectively modified. These nanoclusters showed highly enhanced optical properties owing to the increased electromagnetic fields while the poly (aniline) being used to offer antibody binding capacity. Taking advantages of those properties of the ABPN nanoclusters, surface-enhanced Raman scattering (SERS) intensity-based quantification of two different biomarkers: autoantibodies against cyclic citrullinated peptide and rheumatoid factor was demonstrated using ABPN nanoclusters as SERS nanoprobes. Conclusively, this work has great potential to satisfy a need for multiplexing in diagnosis of early stage of rheumatoid arthritis.

Metformin hydrochloride action on cell membrane N-cadherin expression and cell nucleus revealed by SERS nanoprobes

The anti-tumor effects of metformin hydrochloride (MH), an initial pharmacologic agent for type 2 diabetes, were reexamined by surface-enhanced Raman scattering (SERS) spectroscopy. A SERS immuno-tag fabricated by decorating silver nanoparticles (AgNPs) with a specific antibody was employed to trace the dynamic expression of the tumor metastasis-related N-cadherin. With the MH action, the N-cadherin expression on the cell membranes decreases, proving that MH has a pharmacological effect on prohibiting cancer cell metastasis. Another AgNP-based nucleus targeting nanoprobe was adopted to culture with the MH acted cells, which can help the label-free SERS collection of the cell nuclei to explore the MH influences on intranuclear genes and proteins. By analyzing the intranuclear SERS spectra, the find is that MH has impacts on the transcription and translation of genes, thus regulates the expression of tumor metastasis-related proteins (N-cadherins). This study presents a proof-of-concept for MH as a potential drug for diabetes patients associated with tumors. The developed plasmonic immune analytical platform can be extended to assess other substances of the cell membrane and applicable for the SERS-based screening of membrane receptor-related drugs at the cellular level.

Janus bimetallic nanorod clusters-poly(aniline) nanocomposites with temperature-responsiveness for Raman scattering-based biosensing.

Herein, Janus bimetallic nanorod clusters-poly(aniline) nanocomposites (JRCPCs) with gold nanorod clusters (GNRCs) in side-by-side (SBS) or end-to-end (ETE) configuration are synthesized, and applied to surface-enhanced Raman scattering (SERS)-based biosensing of carcinoembryonic antigen (CEA). Taking advantage of their geometrical and chemical anisotropy, GNRCs in both SBS and ETE configurations are prepared by addition of negatively charged citrate anions and poly(acrylic acid)-block-poly(N-isopropylacrylamide) (PAAc-b-PNIPAM), respectively, to electrostatically interact with cationic cetyltrimethylammonium bromide surfactant on the side of the gold nanorods (GNRs). Subsequently, the JRCPCs are prepared by unidirectional growth of polyaniline and additional growth of Ag onto these GNRCs. JRCPCs with GNRCs in either the SBS or the ETE configuration show strong enhancement of electromagnetic field at both GNR aggregates and GNRC core-Ag shell gaps of bimetallic nanorod cluster components. In particular, because temperature-responsive PAAc-b-PNIPAM of JRCPCs is embedded at GNR junctions, interparticle gaps generated in GNRCs in ETE configuration are controlled via temperature-triggered hydration-dehydration of the PAAc-b-PNIPAM chains such that optical properties are largely changed. With distinct surface functionalities from JRCPCs, SERS-based quantitative analysis of CEA is achieved using JRCPCs as SERS nanoprobes. This work presents the great potential of advanced Janus nanocomposites for SERS-based biosensing applications.

Compartmentalized bimetal cluster-poly(aniline) hybrid nanostructures for multiplexed detection of autoantibodies in early diagnosis of rheumatoid arthritis

Multi-compartmentalized, inorganic-organic hybrid nanostructures have been studied in biomedical applications due to their compositional and structural differences in each compartment. The combination of these hybrid nanostructures with metallic nanoparticle clusters would be attractive due to their interparticle plasmonic coupling for photonics-based biosensing. We herein report a new class of compartmentalized bimetal cluster-poly(aniline) hybrid nanostructures (CBCPHNs) for surface-enhanced Raman scattering (SERS)-based, multiplexed detection of autoantibodies in early diagnosis of rheumatoid arthritis (RA). The bimetallic nanoparticle clusters (BNCs) were prepared in a core-shell form by Raman dye-induced aggregation of gold nanoparticles (GNPs) for the core and reduction of silver ions onto GNP nanoclusters for the shell. Subsequently, CBCPHNs were formed by one-directional growth of poly(aniline) via surface-templated polymerization of aniline monomers as well as additional Ag deposition onto BNCs in the presence of a surfactant. The CBCPHNs showed significant electromagnetic field enhancement at both GNP aggregates and Au core-Ag shell gaps of the BNCs, whereas the poly(aniline) counter-compartment served as a biomolecular conjugation site. In addition, we developed a sandwich-type immunoassay platform using these hybrid nanostructures as SERS nanoprobes and magnetic beads (MBs) for early diagnosis of RA in multiplexing. Autoantibodies against cyclic citrullinated peptide (anti-CCP) and rheumatoid factor immunoglobulin M (RF IgM) were simultaneously detected, and quantified measuring SERS signals of sandwich-type immunocomplexes. Multiplexing of anti-CCP and RF IgM was achieved in low concentration ranges, and their limits of detection were 0.68 IU/mL and 0.93 IU/mL, respectively. These hybrid nanostructures with collective functionalities represent potential nanomaterials for multiplexed detection of autoantibodies.

Alkyne/Ruthenium(II) Complex-Based Ratiometric Surface-Enhanced Raman Scattering Nanoprobe for In Vitro and Ex Vivo Tracking of Carbon Monoxide.

Here, we report a surface-enhanced Raman scattering (SERS) nanosensor for real-time ratiometric detection of carbon monoxide (CO) based on a ligand displacement mechanism. This nanoprobe consists of a gold-silver (Au-Ag) alloy nanoparticle core as the highly active SERS substrate, an alkyne/ruthenium(II) (alkyne/Ru(II)) complex immobilized on the surface as the CO-sensing element, and a porous silica shell to improve the stability and biocompatibility of the particle. Displacement of the alkyne ligand by CO results in a decrease of the alkyne vibrations and an increase of the metal carbonyl complex signals, thus allowing the effective ratiometric detection of CO in real-time. The great potential of this assay for CO detection is validated in clean buffer environments, live cells, and tissue slices.

Polyvinylpyrrolidine-functionalized silver nanoparticles for SERS based determination of copper(II).

A simple, rapid and ultrasensitive surface-enhanced Raman scattering (SERS) assay was developed for detection of Cu2+. It is based on the use of polyvinylpyrrolidine-functionalized silver nanoparticles (AgNPs). Detection is enabled because of the presence of N and O atoms in PVP which have specific coordination capability for Cu2+. Coordination is accompanied by the appearance of the change in the intensity ratio of the 845cm-1 and 899cm-1 peaks (I845/I899) that is associated with pyrrolidinone ring torsion in PVP. The intensity of the band increases linearly in the 0.01 to 2μM Cu2+ concentration range, and the limit of detection is as low as 3nM. The assay potentially is a promising tool for monitoring of Cu2+ in environmental water. Graphical abstract Schematic representation of a method for determination of Cu2+ using polyvinylpyrrolidone-functionalized AgNPs as a SERS nanoprobe. Cu2+ can coordinate with PVP through the N and O atoms. This effect induces AgNP aggregation and affects the electronic structure of PVP. The changes of the Raman spectra are proportional to the Cu2+ concentration.

Reaction Kinetics-Mediated Control over Silver Nanogap Shells as Surface-Enhanced Raman Scattering Nanoprobes for Detection of Alzheimer's Disease Biomarkers.

It is very challenging to accurately quantify the amounts of amyloid peptides Aβ40 and Aβ42, which are Alzheimer's disease (AD) biomarkers, in blood owing to their low levels. This has driven the development of sensitive and noninvasive sensing methods for the early diagnosis of AD. Here, an approach for the synthesis of Ag nanogap shells (AgNGSs) is reported as surface-enhanced Raman scattering (SERS) colloidal nanoprobes for the sensitive, selective, and multiplexed detection of Aβ40 and Aβ42 in blood. Raman label chemicals used for SERS signal generation modulate the reaction rate for AgNGSs production through the formation of an Ag-thiolate lamella structure, enabling the control of nanogaps at one nanometer resolution. The AgNGSs embedded with the Raman label chemicals emit their unique SERS signals with a huge intensity enhancement of up to 107 and long-term stability. The AgNGS nanoprobes, conjugated with an antibody specific to Aβ40 or Aβ42, are able to detect these AD biomarkers in a multiplexed manner in human serum based on the AgNGS SERS signals. Detection is possible for amounts as low as 0.25 pg mL-1 . The AgNGS nanoprobe-based sandwich assay has a detection dynamic range two orders of magnitude wider than that of a conventional enzyme-linked immunosorbent assay.

P-Glycoprotein Detection for Multidrug Resistance of Leukemia Using SERS Immunoassay

Corresponding author: Baoan Chen, MD, PhD; E-mail: cba8888@hotmail.com Zhuyuan Wang, PhD; E-mail: wangzy@seu.edu.cnYiping Cui, PhD; E-mail: cyp@seu.edu.cnKeywords: leukemia; multi-drug resistance; P-glycoprotein; surface-enhanced Raman scattering; SERS intensity.BackgroundAcquisition of multidrug resistance (MDR) in the chemotherapy of leukemia could decrease the survival rate of refractory/relapsing patients. One of the best characterized mechanisms of MDR in leukemia is mediated by multidrug resistance protein-1 and its product, P-glycoprotein (P-gp). Thus, accurate detection of P-gp is necessary for MDR diagnosis. In the recent years, surface-enhanced Raman scattering (SERS) has emerged as a new detection technology of biological label for immunoassay with the advantages of ultrasensitive screening ability and extensive adaptability. However, few researches have focused on the application of SERS immunoassay in the diagnostics of leukemia MDR. The aim of our study is to investigate the expressions of P-gp on the cell surface of K562/ADM cells, and in the whole-blood samples of leukemia using a SERS-based immunoassay technique.MethodsTo simulate the MDR occurrence, we mixed the K562 and K562/ADM cells at different ratios. Besides, we built up the concentration gradient of K562/ADM cells for the quantitative analysis. We also divided 30 blood samples (AML n=14, ALL n=16; female n=12, male n=18; age<60 n=17, age≥60 n=13) into two groups (primary patients in Group A; relapsing patients with over-expressed P-gp in Group B) and compared their SERS-based results with those measured by FCM assay. After preparation of our targeted samples, we synthesized a sandwich immunocomplex, which comprised of magnetic nanobeads (MBs) decorated with anti-CD45, SERS nanoprobes (NPs) decorated with P-gp antibodies, and our targeted samples. Then, SERS measurements were performed on the sandwich immunocomplex. Briefly, the immunocomplex can be precipitated by magnet and the SERS signals could be detected in the precipitates due to the specific binding. Without target samples, only negligible SERS signals could be detected. In this way, the SERS immunoassay can be used to evaluate the presence or expression level of P-gp.ResultsThere were positive and stable SERS signals of peak intensity at 1078 cm-1 after suspended with target samples. First, the SERS intensity of K562/ADM was significantly higher than that of K562 (P <0.01). Second, the SERS intensities of different K562/ADM fractions showed a good linear response to the fractions of K562/ADM cells. Furthermore, the SERS intensities decreased with the decliningK562/ADM concentrations (from 5×106 to 50 cells/mL) and the limit of detection (LOD) could reach 50 cells/ml, which was significantly lower than FCM. Furthermore, the SERS intensity of whole blood samples in Group B were about five folds more than those in Group A (P <0.01). It indicated great application potential and reliability of SERS for MDR assessment in clinic.ConclusionWe have proposed a SERS-based immunoassay to evaluate the expression of P-gp, a product of MDR protein of leukemia. Qualitative and quantitative analysis of K562/ADM indicated excellent specificity, high sensitivity and detection limit, as well as great reproducibility of this immunoassay. It was also demonstrated that this immunoassay was with acceptable accuracy and detection reproducibility for clinical whole blood samples, which was of great importance and convenience for practical clinical application. These features have made SERS-based immunoassay a selective and convenient technique for the identification of leukemia MDR diagnosis. DisclosuresNo relevant conflicts of interest to declare.

A surface-enhanced Raman scattering-based lateral flow immunosensor for colistin in raw milk

A surface-enhanced Raman scattering (SERS)-based lateral flow immunosensor was created to identify colistin in milk. The Raman reporter 5,5-dithiobis-2-nitrobenzoic acid (DTNB) was used to label gold nanoparticles, and then anti-colistin monoclonal antibody (mAb) was attached. The size of the gold nanoparticles in the SERS nanoprobe was optimized, and the amount of DTNB and mAb, the change in hydrodynamic size, zeta potential, and the surface plasmon resonance band were also monitored in the preparation process. The SERS nanoprobe was then applied to a lateral flow strip followed by Raman signal readout for the quantitative determination of colistin with high sensitivity. The limits of detection of this assay were 0.10 ng/mL for colistin in milk, which was far below the previously reported value that was obtained with the ELISA method and the maximum residue limit set by the European Union. The spiking experiment showed high accuracy for this SERS-based immunosensing assay, with a recovery of 88.1%–112.7% and satisfactory assay precision with a standard deviation below 15%. Furthermore, this assay also has the advantage of rapidity, with an assay time less than 20 min. Therefore, these results demonstrate that this SERS-based lateral flow immunosensor is promising for use in the rapid monitoring of colistin in milk.

Microarray surface enhanced Raman scattering based immunosensor for multiplexing detection of mycotoxin in foodstuff

A surface enhanced Raman scattering (SERS) based immunosensor was developed for the detection of three mycotoxins (aflatoxin B1, AFB1; zearalenone, ZEA; ochratoxin A, OTA) in foodstuff. Gold nanoparticles (GNPs) were labeled with 5,5-dithiobis(succinimidyl-2-nitrobenzoate) (DSNB) as Raman reporter and covalently linked with anti-mycotoxin antibodies as SERS nanoprobes, while AFB1-BSA, ZEA-BSA, and OTA-BSA conjugates were covalently linked onto micro-array gold surface as corresponding capture addresses. This design allows three independent immunoreactions multiplexed on a single gold chip. After optimization, the limits of detection of the developed assay are 0.061–0.066 μg/kg for AFB1, 0.53–0.57 μg/kg for ZEA, and 0.26–0.29 μg/kg for OTA in foodstuff. The spiked experiments presented an acceptable assay accuracy with recovery of 83.8%–108.1% and a reasonable assay precision with variation of coefficient less than 15%. Furthermore, the analysis of actual samples by our method demonstrated consistent results by comparison with conventional instrumental analysis. These results indicate that the developed SERS immunosensor can be a promising tool for simultaneously and rapidly monitoring multiple-mycotoxin levels in foodstuff.