Internal Standard Signal Research Articles

Colorimetric and SERS dual-mode detection of GSH in human serum based on AuNPs@Cu-porphyrin MOF nanozyme

BackgroundRapid and accurate detection of glutathione content in human blood plays an important role in real-time tracking of related diseases. Currently, surface-enhanced Raman scattering/spectroscopy (SERS) combined with nanozyme material has been proven to have excellent properties in the detection applications compared to many other methods because of it combines the advantages of trace detection capability of SERS and efficient catalytic activity of nanozymes. However, there are still existing problems in real sample detection, and to achieve quantitative detection is still challenging. ResultsIn this study, gold nanoparticles (AuNPs) were synthesized in situ on the surface of two-dimensional Cu-porphyrin metal-organic framework (MOF) nanosheets to produce the AuNPs@Cu-porphyrin MOF nanozyme, which exhibited both oxidase-like activity and SERS detection ability. On one hand, the intrinsic oxidase-like activity of the nanozyme could be inhibited due to the chelation of glutathione (GSH) and Cu, which thus led to the visual color change of the solution. On the other hand, the abundant Raman “hot spots” at the nanogap generated by Au NPs and the internal standard (IS) signal provided by Cu-meso-tetra (4-carboxyphenyl) porphine (Cu-TCPP) MOF improved the sensitivity and quantitative accuracy of detection. Significance and noveltyA dual-mode signal output sensor based on the nanozyme was thus established, which could be used in the trace detection of GSH. Such a dual-mode sensor possesses excellent detection performance, with the advantage of both wide detection range from 1 to 300 μM in the colorimetric detection mode and high sensitivity with LOD of 5 nM in the SERS detection mode, and can be applied to GSH detection in actual serum samples with reliable results.

3D hierarchic interfacial assembly of Au nanocage@Au along with IS-AgMNPs for simultaneous, ultrasensitive, reliable, and quantitative SERS detection of colorectal cancer related miRNAs

Simultaneous, reliable, and ultra-sensitive analysis of promising miRNA biomarkers of colorectal cancer (CRC) in serum is critical for early diagnosis and prognosis of CRC. In this work, we proposed a novel 3D hierarchic assembly clusters-based SERS strategy with dual enrichment and enhancement designed for the ultrasensitive and quantitative analysis of two upregulated CRC-related miRNAs (miR-21 and miR-31). The biosensor contains the following: (1) SERS probe, Au nanocage@Au nanoparticles (AuNC@Au NPs) labeled with Raman reporters (RaRs). (2) magnetic capture unit, Ag-coated Fe3O4 magnetic nanoparticles (AgMNPs) modified with internal standard (IS). (3) signal amplify probes (SA probes) for the formation of hierarchic assembly clusters. Based on this sensing strategy, the intensity ratio IRaRs/IIS with Lg miRNAs presents a wide linear range (10 aM–100 pM) with a limit of detection of 3.46 aM for miR-21, 6.49 aM for miR-31, respectively. Moreover, the biosensor shows good specificity and anti-interference ability, and the reliability and repeatability of the strategy were then verified by practical detection of clinical serum. Finally, the biosensor can distinguish CRC cancer subjects from normal ones and guide the distinct tumor, lymph node, and metastasis (TNM) stages. Overall, benefiting from the face-to-face coupling of hierarchic assembly clusters, rapid magnetic enrichment and IS signal calibration of AgMNPs, the established biosensor achieves ultra-sensitive and simultaneous detection of dual miRNAs and opens potential avenues for prediction and staging of CRC.

Development of magnetic fluorescence aptasensor for sensitive detection of saxitoxin based on Fe3O4@Au-Pt nanozymes

In this work, on the basis of Fe3O4@Au-Pt nanozymes (MAP NZs) and aptamer recognition, a magnetic fluorescent aptasensor (MFA) was developed for sensitive and accurate detection of saxitoxin (STX). With the bridge of STX aptamer (AptSTX) and complementary DNA (cDNA), AptSTX decorated MAP NZs (MAP/Apt) and cDNA modified green quantum dots (cDNA@g-QDs) were connected to form MAP/Apt-cDNA@g-QDs complex. As STX behaves a strong binding ability towards AptSTX, it will compete with cDNA and hybridize with Apt to release cDNA@g-QDs. With the addition of TMB, MAP will catalyze TMB to the oxidized TMB (ox-TMB), thereby quenching the fluorescence of g-QDs due to the inner filter effect. Based on this finding, the quantitative relationship between the change in fluorescence of gQDs and STX concentration was explored with a limit of detection (LOD, S/N = 3) of 0.6 nM. An internal standard signal of oxTMB was adopted and reduced the fluctuation of fluorescence signal output. Besides, the fluorescence probe can selectively recognize and detect STX among five marine toxins. Eventually, the MFA method behaved good performance in detecting seafood samples with recoveries of 82.0 % ∼ 102.6 % as well as coefficient of variations (CV) of 7.2 % ∼ 10.3 %. Therefore, the method with internal signal is hopeful to be a potential candidate for sensitive and accurate detection of STX in seafood.

Highly sensitive SERS sensors for glucose detection based on enzyme@MOFs and ratiometric Raman

Diabetes is a common chronic metabolic disease. The frequent fluctuation of glucose is the main cause of most diabetes complications, which in turn causes harm to the health of patients. Surface-enhanced Raman scattering (SERS) spectroscopy has attracted much attention in the rapid detection of glucose due to its unique molecular fingerprinting ability, ultra-high sensitivity and fast response. However, due to the low affinity between glucose and SERS substrate, poor signal, susceptibility to complex environmental interference, and poor stability of SERS detection, it is still a challenge for SERS to accurately and sensitively determine glucose in complex environments. In this work, we encapsulated 4-mercaptobutyronitrile (4-MBN) as an internal standard (IS) in Au@Ag NRs inside and then Au@4-MBN@Ag NRs, Leucomalachite Green (LMG), glucose oxidase (GOx) and horseradish peroxidase (HPR) were encapsulated in ZIF-8 to prepare a tandem enzyme catalytic ratiometric SERS sensor Au@4-MBN@Ag@LMG@ZIF-8(GOx, HPR) for the detection of glucose in saliva. Because ZIF-8 enhanced the catalytic activity of the enzyme, the ability of glucose enrichment, and weakens the aggregation of Ag NRs. The internal standard signal molecule improves the accuracy and sensitivity of detection. The ratiometric Raman signal I412/I2233 of glucose has a good linear relationship with the concentration in the range of 0.1–100 μM, and the limit of detection (LOD) could be down to 0.03 μM. At the same time, it has excellent selectivity, repeatability and accuracy. The recovery rate of glucose in saliva is 96.50%–105.56 %, which proves the feasibility of the method. The Au@4-MBN@Ag@LMG@ZIF-8(GOx, HPR) sensor prepared in this study showed excellent SERS performance, which was able to detect glucose quickly, sensitively and accurately. This work provides a new strategy for the design of enzyme-catalyzed SERS sensors.

Thiol-ene click derivatization reaction coupled with ratiometric surface-enhanced Raman scattering for reproducible and accurate determination of acrylamide.

Acrylamide (AA) is a carcinogen mainly ingested through food and drinking water, making its accurate determination crucial for both food safety and environmental protection. Herein, we proposed a derivatization-based ratiometric surface-enhanced Raman scattering (SERS) method for the quantification of AA. High density Au NPs were anchored to the surface of Cu-TCPP MOF nanosheets (MOFNs) to form the SERS sensor. The abundant Raman "hot spots" at the nanogaps generated by the Au NPs and the internal standard (IS) signal provided by Cu-TCPP MOFNs improved the sensitivity and quantitative accuracy of the method. Following the thiol-ene click derivatization reaction between p-aminothiophenol (PATP) and AA, the Raman peak intensity ratio (I1080/I395) was employed to quantify AA. The linear range was 0.1nM to 10μM, and the limit of detection (LOD) was as low as 0.08nM. Trace amounts of AA in food and water samples were successfully determined using this method.

Portable SERS-based lateral flow immunoassay strips with self-calibration for detection of a prostate cancer biomarker

Serum prostate-specific antigen (PSA) is thought to be the most vital indicator for early identification, staging and monitoring of prostate cancer (PCa). Although lateral flow immunoassay (LFA) has demonstrated limitless promise for point-of-care testing (POCT) and has drawn increasing interest and attention, there are significant restrictions on the assay's sensitivity and quantitative capability. Surface-enhanced Raman spectroscopy-based LFA (SERS-LFA) technique integrates the great sensitivity of SERS with the simplicity, rapidity, and usability of the LFA technique, making it ideal for POCT. In this paper, we propose a sensitive self-calibrating SERS-LFA platform, which uses Au@MBN@Ag@PSA NPs as a SERS immunoprobe for the specific recognition of PSA and loads graphene oxide/gold nanoparticles (GO/Au NPs) on nitrocellulose (NC) membranes as an internal standard (IS) molecule. The SERS-LFA platform's detection accuracy is increased through dynamic calibration of the characteristic signals, which is accomplished by detecting the immunoprobe and IS signals simultaneously and computing their respective signal intensity ratios. The self-calibrated SERS-LFA platform demonstrated a 1.65-fold improvement in reproducibility over the conventional SERS-LFA, and PSA could only be detected to a limit of 0.08 ng/mL, meaning that it was 3.5-fold lower than the conventional SERS-LFA platform. The spike recovery experiments yielded recoveries of 96.16∼104.53% with RSD values of 9.37%, 8.66%, and 3.49%, respectively, demonstrating that our self-calibrated SERS-LFA platform for PSA quantification has an acceptable level of precision and has great prospect for early screening of PCa and other diseases.

Lanthanide coordination carbon quantum dots construct a ratiometric fluorescent sensor for the detection of norfloxacin in milk

The residues of norfloxacin in milk and other foods cause serious harm to human health. Compared with the other ratiometric fluorescence sensors formed by lanthanide hybridized carbon quantum dots, the synthesized carbon quantum dot of this sensor used citric acid as the carbon precursor. It could act as an internal standard signal (λem = 460 nm) and form ratiometric fluorescence with a Tb3+ characteristic emission peak (λem = 545 nm). More importantly, this carbon quantum dot could sensitize Tb3+ to promote the f-f transition of Tb3+ and enhance its characteristic fluorescence. In addition, the antenna effect between norfloxacin and Tb3+ could further enhance the fluorescence signal at 545 nm. Under the optimal detection conditions, the limit of detection was down to 3.20 nM, and the recovery rate in milk was 94.60–97.00 %. The sensor platform showed a rapid and sensitive response to norfloxacin, providing a simple and effective strategy for the detection of antibiotics in food.

A pH-responsive sensor based on intramolecular internal standard for reproducible detection of strong acids and bases via 19F NMR spectroscopy

Numerous methods, including pH meters and optical sensors, have been developed for the detection of pH, which is an important indicator in various fields. However, those methods are susceptible to errors in strongly acidic and basic ranges and inaccurate pH measurement due to sample turbidity, hindering their application such as photographic industries and wastewater treatment facilities. Eco-friendly and non-invasive 19F NMR spectroscopy is a promising technique for measurement of strong acids and bases owing to its high sensitivity and little interference; nevertheless, inconsistencies in reproducibility impede its widespread adoption. Herein, we developed a19F NMR-based pH sensor by introducing an intramolecular internal standard strategy into a pH-responsive fluorinated material. Based on the acceptable deviation (ΔδF = 17−19 ppb) in the evaluation of the internal standard signal, this pH-sensing platform enabled reproducible pH measurements in strongly acidic and basic environments. Moreover, its 19F NMR response showed reversibility and high stability to potential interfering factors, and the low absolute difference (0.026−0.086 in pH) for real samples such as diet Coke suggests its potential suitability for various acidic beverages.

Molecularly imprinted polymers embedded with double perovskite quantum dots: A ratiometric fluorescence sensor for visible and fluorescent determination of Rhein

A ratiometric fluorescence sensor based on molecularly imprinted polymers embedded with double perovskite quantum dots (green fluorescent CsPbBr3 (GPQDs) and red fluorescent CsPbI3 (RPQDs)) were prepared for the visible and fluorescent determination of Rhein. Double perovskite quantum dots were synthesized by a one-pot method with in-situ hydrolysis, and the fluorescent probes containing GPQDs and RPQDs with molecularly imprinted cavities (MIPs@RPQDs/GPQDs@SiO2) were synthesized by sol gel method. And the synthesized MIPs@RPQDs/GPQDs@SiO2 can emit two stable and independent fluorescence peaks at 520 nm with green fluorescence and at 695 nm with red fluorescence respectively. Since Rhein could specifically quench the red fluorescence without affecting the green fluorescence at 520 nm, a ratiomitric fluorescence sensor could be and was constructed with GPQDs as the internal standard signal and the RPQDs as the response signal. The sensor had a good linear relationship with the concentration of Rhein between 15 and 135 nM, and the detection limit was 1.90 nM (S/N = 3). Moreover, Rhein could be detected by observing the color transformation of the fluorescent probe directly with naked eyes. In addition, Rhein in the traditional Chinese medicine Rheum palmatum L. had been detected by the constructed ratiometric fluorescene probe with satisfactory.

A new LC‐MS/MS assay for the quantification of Aβ40 and Aβ42 in plasma: validation and clinical performance

AbstractBackgroundEarly detection of Alzheimer’s disease (AD) represents an unmet clinical need. Cerebrospinal fluid (CSF) biomarkers can potentially fulfil this need, but specimen collection is invasive. Blood‐derived biomarkers are preferable, and several studies have shown an association between the Aβ42/40 ratio and amyloid PET status. However, blood diagnostic tests for AD are challenging due to interlaboratory differences in analytical techniques and preanalytical handling. Here we describe the development and validation of a LC‐MS/MS assay to quantify Aβ40 and Aβ42 from plasma and assess clinical performance.MethodAβ40 and 42 peptides were simultaneously immunoprecipitated prior to protein digestion and LC‐MS/MS analysis. Blood collection studies were conducted to determine the optimal specimen type, tube type, and storage conditions. Clinical validation studies were performed in a cohort of 209 clinically assessed individuals with PET data (67 cognitively normal, 66 with early MCI, 37 with late MCI, and 39 with AD).ResultBoth Aβ40 and 42 showed a linear measurement range of 10‐2500 pg/mL, with R2 values ≥0.99. Assay precision ranged from 2.6‐9.0% for Aβ40, Aβ42, and Aβ42/40. Plasma specimens were stable for up to 5 freeze‐thaw cycles, 6 hours at room temperature, 5 days refrigerated, at least 32 days frozen and 9 months at ultra‐low temperature. Compared to other tube types, blood collected in K2EDTA tubes had an average analyte response that was 1.6‐fold higher for both Aβ40 and 42 (range 1.4‐4.0 fold). Peptide recovery was higher in plasma than in serum (1.2‐1.4 fold higher for Aβ40 and 42). Variation in the internal standard signal, a measure of overall assay variability, was <10% for K2EDTA compared to >20% for other tube types (range 24.6‐33.3%). The test accurately differentiated PET‐positive from PET‐negative individuals (AUROC=0.862 95% CI 0.814‐0.910). At the Aβ42/40 cut‐point of 0.160, the assay has a sensitivity of 71% and specificity of 89% for detecting PET‐positivity, which is suggestive of AD.ConclusionWe optimized the analytical performance of an LC‐MS/MS assay for plasma Aβ40 and Aβ42. Preanalytical factors, including specimen collection tube types, were key for reproducible and accurate quantification. Performance characteristics were similar to those reported in the literature using CSF specimens.

Quantitative SERS sensing mediated by internal standard Raman signal from silica nanoparticles in flexible polymer matrix

Attributed to poor signal uniformity and external interference, ultrasensitive surface-enhanced Raman spectroscopy (SERS) still faces difficulties in the reliable and quantitative detection of trace molecules. Here, a facile Ag/Si/sodium carboxy methyl cellulose (NaCMC) film with internal standard (IS) was promoted for quantitative determination of thiram. The effects of preparation conditions on SERS activity of the film were systematically investigated and then a flexible SERS substrate with high sensitivity and uniformity was fabricated. The enhancement factor was calculated to be 1.12 × 106 and SERS mapping was recorded with a relative standard deviation value of 19.8% by utilizing 4-mercaptobenzoic acid (4-MBA) as target molecule. Additionally, the dominant contribution of the IS from encapsulated Si nanoparticles (NPs) was confirmed in the quantitative assay of 4-MBA and thiram, facilitating attractive fitting coefficients (R2) as 0.991 and 0.998. Besides that, the proposed flexible film was conducted to scrub trace thiram from the surfaces of apple, orange, and cucumber, resulting in recoveries of 89%, 94%, and 91%. A smart and facile quantitative SERS substrate was developed here for monitoring trace biochemical molecules, verifying its potential utilizations in monitoring pesticide residues.

A Negative Internal Standard in Urinary Metanephrines Quantification.

A 67-year-old woman was sent to the cardiology department for a Staphylococcus aureus infective endocarditis treated with cefazolin. In view of her severe arterial hypertension resistant to triple therapy and the discovery of an adrenal nodule, urinary metanephrines were ordered. Quantification of metanephrines was performed by HPLC with electrochemical detection, following the instructions of the Chromsystems® Metanephrines in Urine kit. Instead of a positive peak for the internal standard, 4-hydroxy-3-methoxybenzylamine, a negative peak appeared in the patient’s chromatogram (Fig. 1), preventing the quantification of metanephrines. ... ... Interferences for urinary metanephrines determination mainly include a catecholamine-rich diet and drugs involved in catecholamine metabolism (1). Paracetamol and amoxicillin are also known to interfere with electrochemical detection (1, 2). 4-Hydroxy-3-methoxybenzylamine (in curry) (3) and methenamine (4) alter the internal standard signal. We determined here that cefazolin, which is mainly eliminated unchanged in urine and has electrochemical properties (5), turned the peak negative, which we confirmed by adding cefazolin to urine and water. If interference from cefazolin was suspected, one could use mass spectrometry or an alternative internal standard for accurate quantification.

Quantitative Visual Detection of Mercury Ions With Ratiometric Fluorescent Test Paper Sensor.

A novel ratiometric fluorescence probe based on nitrogen-doped blue carbon dots (NCDs) and red gold nanoclusters (Au NCs) for mercuric ion (Hg2+) has been prepared and characterized. A user friendly fluorescent test paper based sensor combined with smartphone was fabricated for rapid visual and quantitative detection. Hg2+ can specifically bind to Au+ on the surface of Au NCs, leading to the quench of red fluorescence while the fluorescence intensity of the NCDs with blue fluorescence remained unchanged as a internal standard signal. The implement of paper-based sensor address some common drawback in analytical process such as the detection time, analysis cost. In a further demonstration, a homemade detection device with smartphone was used to qualify the Hg2+. After adding different concentration of Hg2+, red, purple, and blue colors were obtained on the detection zones of the fluorescent test paper. The Android App Color Grab was used to identify the red, green and blue (RGB) values of fluorescent color. The rapid visual and quantitative detection of Hg2+ was accomplished with the detection limit of 2.7 nM for fluorescence, 25 nM for smartphone and 32 nM for paper strip. The developed multi-mode detection platform was successfully applied to the detection of mercury ions in water samples with acceptable recoveries. The NCDs and Au NCs probe facilitate the one-site environmental monitoring for Hg2+ with “naked-eye” and smartphone.

Quantifying H2O2 by ratiometric fluorescence sensor platform of N-GQDs/rhodamine B in the presence of thioglycolic acid under the catalysis of Fe3+

In the presence of thioglycolic acid (TGA) and under the catalysis of Fe3+, a simple, rapid, sensitive, selective and effective ratiometric fluorescence sensor platform based on the mixed physically blue nitrogen-doped graphene quantum dots (N-GQDs) as probe signals and orange rhodamine B as internal standard signals has been constructed for analysis of H2O2 in human serum. TGA is the key factor for fluorescence response toward H2O2 by N-GQDs and the mechanism is H2O2 reacts speedily with TGA under the catalysis of Fe3+, and produces intermediate of superoxide anions (O2−), which accepts electrons from N-GQDs, and generates graphene oxide, causing the fluorescence quench of N-GQDs. Compared with N-GQDs probe, the sensitivity of the ratiometric fluorescence sensor platform of N-GQDs/rhodamine B for analysis of H2O2 has been improved by nearly 5-folds. Under the optimum conditions, Fλ=580nm/Fλ=440nm has a good linear relationship with the concentration of H2O2 and the detection limit of H2O2 is 0.46 μmol/L with 3.5% RSD. The established sensor platform has been successfully used for probing H2O2 in human serum with satisfactory results. The superior performance of the probe lies in its high selectivity and can be directly employed in detecting H2O2 in serum samples without any sample pretreatment procedures.

NMR internal standard signal shifts due to cyclodextrin inclusion complexes.

Nuclear magnetic resonance (NMR)-based screening of materials is a powerful tool for quality control, authenticity testing, and purity testing of compounds. However, reliance on 3-(trimethylsilyl)-propane-1-sulfonate (DSS) and 3-(trimethylsilyl)propanoic acid (TMSP) for referencing the spectra of aqueous samples is not without hazard, particularly with automated analyses. The assumption that these reference signals always represent 0ppm is ubiquitous in NMR spectroscopy and is routinely used for spectral alignment. However, it has been found that cyclodextrins readily generate inclusion complexes with DSS and TMSP with the effect of rendering this assumption incorrect. These inclusion complexes alter the electronic shielding of the trimethylsilane functional groups on DSS and TMSP yielding a small, but significant, shift to a higher frequency in the signal relied upon for spectral referencing. As a result, samples containing traces of these compounds may be incorrectly declared fraudulent, inconsistent with standards, or adulterated. In order to maintain the viability of this screening method, vigilance and/or improved referencing of spectra is needed.

Quantification of Teicoplanin Using the HPLC-UV Method for Clinical Applications in Critically Ill Patients in Korea.

A high-performance liquid chromatography-ultraviolet detector (HPLC-UV) method has been used to quantify teicoplanin concentrations in human plasma. However, the limited analytical accuracy of previously bioanalytical methods for teicoplanin has given rise to uncertainty due to the use of an external standard. In this study, an internal standard (IS), polymyxin B, was applied to devise a precise, accurate, and feasible HPLC-UV method. The deproteinized plasma sample containing teicoplanin and an IS of acetonitrile was chromatographed on a C18 column with an acidic mobile phase consisting of NaH2PO4 buffer and acetonitrile (78:22, v/v) by isocratic elution and detection at 220 nm. The linearity was in the range 7.8–500 mg/L calculated by the ratio of the teicoplanin signal to the IS signal. This analytical method, validated by FDA guidelines with ICH Q2 (R1), was successfully applied to analyze the plasma samples of patients in the intensive care unit for treating serious resistant bacterial infectious diseases, such as those by methicillin-resistant Staphylococcus aureus and Enterococcus faecalis. The methods suggested the potential for use in routine clinical practice for therapeutic drug monitoring of teicoplanin, providing both improved accuracy and a wide range of linearity from lower than steady-state trough concentrations (10 mg/L) to much higher concentrations.

A data-driven approach for the detection of internal standard outliers in targeted LC-MS/MS assays

Heavy-labelled internal standard (IS) compounds are commonly used in liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays to control for stochastic and systematic variation. Identifying samples that suffer from unwanted variation is critically important in order to avoid factitiously inaccurate results. Current approaches for outlier detection typically employ arbitrary thresholds and ignore systematic drift. To improve this, we applied robust linear mixed-effects models (LMMs) to capture the within- and between-run variability in IS signal and generate data-driven acceptance ranges for routine use.Data from in-house LC-MS/MS assays for 25-hydroxyvitamin D3and D2 and prednisolone were retrospectively collected. The variation in the percentage deviation of the internal standard area from the mean of the calibrators was modelled through the use of robust LMMs. The fitted LMMs revealed significant positive drift in IS signal over the analytical runs for vitamin D, with slope coefficients of 0.118 (95% CI: 0.098, 0.138) and 0.192 (0.168, 0.215) for D3 and D2, respectively. In contrast, the models for prednisolone demonstrated a significant negative drift in IS signal, with a slope coefficient of −0.164 (−0.297, −0.036). Non-parametric, cluster bootstrap resampling enabled us to define acceptance ranges for use in future assays.Here, we have described a computational approach to extensively characterise the variation in IS signal in routinely-performed LC-MS/MS assays. This approach facilitates a robust quality assessment of IS outliers in routine practice and thus has the potential to improve patient safety. Importantly, this approach is applicable to other MS assays where linear variation in IS signal is observed.

On-Site and Quantitative Detection of Trace Methamphetamine in Urine/Serum Samples with a Surface-Enhanced Raman Scattering-Active Microcavity and Rapid Pretreatment Device.

Here, it reports a high-throughput detection method for reliably quantitative analysis of illegal drugs in complex biological samples by means of a surface-enhanced Raman scattering (SERS) active microcavity and rapid pretreatment device. Based on the well-made hemispherical microcavities that regularly distributed on a glass array, the quality-controllable microcavity device is fabricated by the compact self-assembly of core-shell nanopeanuts (CSNPs) onto the inside surface. Both the CSNPs with a quantifiable internal standard signal of crystal violet acetate anchored inside their gap and the well-made microcavity referred to the physical amplification of the microscale groove surface will do well in trace analysis, which will allow us to realize the accurately quantitative SERS analysis of targeted analytes spread on the bottom area of the microcavity array. As an example, 0.8 nM malachite green and 160 ppb methamphetamine (MATM) have been successively detected in a wide range as standard, while even 0.01 ppm MATM mixed in the urine/serum samples has been efficiently tested by the microcavity device equipped with a rapid pretreatment device (manual monolithic column syringe needle). All of the above suggest that the SERS-active microcavity equipped with a rapid pretreatment device has potential in the on-site quick test of trace amounts of illegal drugs in bodily fluid samples or other field analysis of food sanitation, environmental safety, and public health.

S,N-Doped carbon dots for tetracyclines sensing with a fluorometric spectral response

S,N-doped carbon dots (S,N-CDs) were facilely prepared via a hydrothermal method by using thiourea and citric acid (CA) as precursors. The as-prepared S,N-CDs exhibited high stability in aqueous solution and were applied for fluorometric detection of tetracyclines (TCs). The approach was developed on the basic of the fluorescence of S,N-CDs at 440 nm, which was selectively quenched by TCs through the inner filter effect (IFE) mechanism. Moreover, the fluorescence of TCs with maximum at 600 nm could be used as the internal standard signal, resulting in a fluorometric spectral response. The limit of detection (LOD) was 0.25, 0.39 and 0.26 μM for tetracycline (TC), doxycycline (DC) and oxytetracycline (OTC), respectively. Furthermore, S,N-CDs were successfully utilized for the detection of residual TCs in fish and pork samples with acceptable recovery and good RSD.

Gold Nanorod Array-Bridged Internal-Standard SERS Tags: From Ultrasensitivity to Multifunctionality.

Bimetallic gold core-silver shell (Au@Ag) surface-enhanced Raman scattering (SERS) tags draw broad interest in the fields of biological and environmental analysis. In reported tags, silver coating tended to smooth the surface and merge the original hotspot of Au cores, which was disadvantageous to signal enhancement from the aspect of surface topography. Herein, we developed gold nanorod (AuNR)-bridged Au@Ag SERS tags with uniform three-dimensional (3D) topography for the first time. This unique structure was achieved by selecting waxberry-like Au nanoparticles (NPs) as cores, which were capped by vertically oriented AuNR arrays. Upon selective surface blocking with thiol-ligands, Ag NPs were controlled to anisotropically grow on the tips of the AuNRs, producing high-density homo- (Ag-Ag) and hetero- (Au-Ag) hotspots in a single NP. The 3D hotspots rendered this NP extraordinary SERS enhancement ability (an analytical enhancement factor of 3.4 × 106) 30 times higher than the counterpart with a smooth surface, realizing signal detection from a single NP. More importantly, multiplexing signals ("blank" or multiplex "internal standard") can be achieved by simply changing thiol-ligands, as exemplified in the synthesis of NPs with 8 signatures. Furthermore, the multifunctionality has been demonstrated in living cell/in vivo imaging, photothermal therapy, and SERS substrates for ratiometric quantitative analysis, relying on the inherent internal standard signal. The prepared Au@Ag NPs have great potential as standard tools in many SERS-related fields.