In this paper, CdS quantum dots (QDs) were synthesized. Positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged CdS quantum dots were sequentially adsorbed on the surface of graphene oxide (GO). The nano-luminescent materials GO-QDs were prepared and characterized by UV–Vis absorption spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The GO-QDs were then modified on the surface of glassy carbon electrode (GCE). Chloramphenicol aptamer (apt) of 5′-end modified biotin hybridized with the aptamer complementary strand (cDNA) of 5′-end modified amino group into double-stranded DNA (dsDNA). The double-stranded DNA was bonded onto the surface of GO-QDs modified electrode. When the electrode was incubated with streptavidin - labeled horseradish peroxidase (SA-HRP), the biotin modified at the end of the chloramphenicol aptamer can specifically bind directly to the streptavidin labeled HRP. Therefore, HRP was bonded to the surface of the electrode. Hydrogen peroxide was used as the co-reactant of the QDs. HRP can thereby consume hydrogen peroxide and can weaken the electrochemiluminescence intensity. Chloramphenicol in solution can specifically bind to the aptamer to form a composite and to unwind the dsDNA. Then the composite was detached from the surface of the electrode. HRP also left the electrode surface along with the aptamer, so that the electrochemiluminescence signal was significantly enhanced. The electrochemiluminescence intensity of the sensor showed a linear correlation with the logarithm of chloramphenicol concentration. The linear range was 1.0 × 10−12–1.0 × 10−7 M, the detection limit is 0.5 pM. The reproducibility, stability and specificity of the sensor were also studied. The sensor was used for the determination of chloramphenicol in samples and satisfactory results were obtained.

An electrochemical sensor is described for the determination of nadifloxacin (NF). A glassy carbon electrode (GCE) was modified with amino-functionalized multiwalled carbon nanotubes and titanium dioxide nanoparticles. The modified GCE was characterized by electrochemical impedance spectroscopy, cyclic voltammetry and scanning electron microscopy. The electro-oxidation of NF follows a pH-dependent irreversible behavior. The effects of pH value, scan rate, supporting electrolyte, accumulation potential and accumulation time were optimized. Under optimum conditions and at a typical working potential of 600 mV (vs. Ag/AgCl), the adsorptive stripping voltammetric response is linear in the 5 nM to 5.0 μM NF concentration range. The limit of detection is 1.69 × 10−10 M in acidic solution of pH 1. The selectivity was investigated in the presence of 1–1000-fold concentrations of potentially interfering agents. Recoveries from cream formulations spiked with NF were performed to study precision and accuracy.

The aim of any scientific discussion is to get closer to the truth and remove any obstruction impeding the progress of science. It is with this intention in mind that I endeavour to write a short reply to Fletcher's short communication and show that Fletcher is wrong in his criticisms of our recent publication.

Thin film rotating-ring disc electrode (RRDE) technique is exploited to quantify the parasitic hydrogen evolution reaction (HER) competing with the desired V3+-reduction at surface modified carbon nanoparticles for application as electrocatalysts in the negative half-cell of vanadium redox-flow batteries (VRFB). Carbon based electrode materials are derived from standard Vulcan XC-72 carbon, treated by chemical surface etching techniques proposed for carbon felt-electrodes in the literature. Additional electrochemical characterization is performed using stationary cyclic voltammetry (CV) followed by fitting of CV data, Fourier-transform alternating-current cyclic voltammetry (FT-ACCV) and electrochemical impedance spectroscopy (EIS) followed by distribution of relaxation times (DRT) analysis. To our knowledge the present paper is the first study using the RRDE technique for separating HER and V3+-reduction reactions. It is demonstrated that the ratio of HER to V3+-reduction significantly depends on the chemical pretreatment of the carbon electrodes and that the V3+-reduction proceeds at an optimum rate at E − ERHE = −0.45 V. Separating the HER from the V3+-reduction also allows us to provide highly accurate values for the diffusion coefficient of the V3+-ion in sulfuric acid solutions.

In a recent paper in this journal, M.Y. Abyaneh, M. Fleischmann, and M.H. Mehrabi claimed to have developed a novel approach towards the derivation of the current-time profile of a single hemispherical crystal growing under mixed kinetic-diffusion control. Subsequently, their claim was disputed by S. Fletcher, and the present document contains his closing remarks on the ensuing discussion.

Abstract Post-translational modifications (PTMs) play critical roles in biological processes and have significant effects on the structures and dynamics of proteins. Top-down proteomics methods were developed for and applied to the study of intact proteins and their PTMs in human samples. However, the large dynamic range and complexity of human samples makes the study of human proteins challenging. To address these challenges, we developed a 2D pH RP/RPLC-MS/MS technique that fuses high-resolution separation and intact protein characterization to study the human proteins in HeLa cell lysate. Our results provide a deep coverage of soluble proteins in human cancer cells. Compared to 225 proteoforms from 124 proteins identified when 1D separation was used, 2778 proteoforms from 628 proteins were detected and characterized using our 2D separation method. Many proteoforms with critically functional PTMs including phosphorylation were characterized. Additionally, we present the first detection of intact human GcvH proteoforms with rare modifications such as octanoylation and lipoylation. Overall, the increase in the number of proteoforms identified using 2DLC separation is largely due to the reduction in sample complexity through improved separation resolution, which enables the detection of low-abundance PTM-modified proteoforms. We demonstrate here that 2D pH RP/RPLC is an effective technique to analyze complex protein samples using top-down proteomics.

Abstract The analysis of histone post-translational modifications (PTMs) by mass spectrometry (MS) has been critical to the advancement of the field of epigenetics. The most sensitive and accurate workflow is similar to the canonical proteomics analysis workflow (bottom-up MS), where histones are digested into short peptides (4-20 aa) and quantitated in extracted ion chromatograms. However, this limits the ability to detect even very common co-occurrences of modifications on histone proteins, preventing biological interpretation of PTM crosstalk. By digesting with GluC rather than trypsin, it is possible to produce long polypeptides corresponding to intact histone N-terminal tails (50-60 aa), where most modifications reside. This middle-down MS approach is used to study distant PTM co-existence. However, the most sensitive middle-down workflow uses weak cation exchange-hydrophilic interaction chromatography (WCX-HILIC), which is less robust than conventional reversed-phase chromatography. Additionally, since the buffer systems for middle-down and bottom-up proteomics differ substantially, it is cumbersome to toggle back and forth between both experimental setups on the same LC system. Here, we present a new workflow using porous graphitic carbon (PGC) as a stationary phase for histone analysis where bottom-up and middle-down sized histone peptides can be analyzed simultaneously using the same reversed-phase buffer setup. By using this protocol for middle-down sized peptides, we identified 406 uniquely modified intact histone tails and achieved a correlation of 0.85 between PGC and WCX-HILIC LC methods. Together, our method facilitates the analysis of single and combinatorial histone PTMs with much simpler applicability for conventional proteomics labs than the state-of-the-art middle-down MS.

Abstract Proteins physiologically exist as “proteoforms” that arise from one gene and acquire additional function by post-translational modifications (PTM). When multiple PTMs coexist on single protein molecules, top-down proteomics becomes the only feasible method of characterization; however, most top-down methods have limited quantitative capacity and insufficient throughput to truly address proteoform biology. Here we demonstrate that top-down proteomics can be quantitative, reproducible, sensitive, and high throughput. The proteoforms of histone H4 are well studied both as a challenging proteoform identification problem and due to their essential role in the regulation of all eukaryotic DNA-templated processes. Much of histone H4’s function is obfuscated from prevailing methods due to combinatorial mechanisms. Starting from cells or tissues, after an optimized protein purification process, the H4 proteoforms are physically separated by on-line C3 chromatography, narrowly isolated in MS1 and sequenced with ETD fragmentation. We achieve more than 30 replicates from a single 35-mm tissue culture dish by loading 55 ng of H4 on column. Parallelization and automation yield a sustained throughput of 12 replicates per day. We achieve reproducible quantitation (average biological Pearson correlations of 0.89) of hundreds of proteoforms (about 200–300) over almost six orders of magnitude and an estimated LLoQ of 0.001% abundance. We demonstrate the capacity of the method to precisely measure well-established changes with sodium butyrate treatment of SUM159 cells. We show that the data produced by a quantitative top-down method can be amenable to parametric statistical comparisons and is capable of delineating relevant biological changes at the full proteoform level.

Abstract Reversible phosphorylation plays critical roles in cell growth, division, and signal transduction. Kinases which catalyze the transfer of γ-phosphate groups of nucleotide triphosphates to their substrates are central to the regulation of protein phosphorylation and are therefore important therapeutic targets. Top-down mass spectrometry (MS) presents unique opportunities to study protein kinases owing to its capabilities in comprehensive characterization of proteoforms that arise from alternative splicing, sequence variations, and post-translational modifications. Here, for the first time, we developed a top-down MS method to characterize the catalytic subunit (C-subunit) of an important kinase, cAMP-dependent protein kinase (PKA). The recombinant PKA C-subunit was expressed in Escherichia coli and successfully purified via his-tag affinity purification. By intact mass analysis with high resolution and high accuracy, four different proteoforms of the affinity-purified PKA C-subunit were detected, and the most abundant proteoform was found containing seven phosphorylations with the removal of N-terminal methionine. Subsequently, the seven phosphorylation sites of the most abundant PKA C-subunit proteoform were characterized simultaneously using tandem MS methods. Four sites were unambiguously identified as Ser10, Ser11, Ser18, and Ser30, and the remaining phosphorylation sites were localized to Ser2/Ser3, Ser358/Thr368, and Thr[215-224]Tyr in the PKA C-subunit sequence with a 20mer 6xHis-tag added at the N-terminus. Interestingly, four of these seven phosphorylation sites were located at the 6xHis-tag. Furthermore, we have performed dephosphorylation reaction by Lambda protein phosphatase and showed that all phosphorylations of the recombinant PKA C-subunit phosphoproteoforms were removed by this phosphatase.

Abstract Methylation of proteins has considerable impacts on physiological processes including signal transduction, DNA damage repair, transcriptional regulation, gene activation, and inhibition of gene expression. However, the traditional proteomics-based approach suffers from limited identification rates of these critical methylation sites on endogenous peptides. In this work, a peptidomics-based workflow was established to discover and characterize the global methylome of endogenous peptides in human cells. The reliability of our strategy was validated by methyl-SILAC labeling, resulting in 83% true-positive identifications in the HeLa cell line. We applied this approach to seven human cell lines, and 700 methylated forms on 646 putative methylation sites were identified in total, with over 61% of the methylation sites being newly identified. This study provides a complementary strategy for a traditional proteomics-based approach that enables identification of missing methylation sites and creates a first methylome draft of endogenous peptides of human cell lines, offering a valuable resource for in-depth studies of biological functions of methylated endogenous peptides.

Abstract Histone post-translational modifications (PTMs) have been intensively investigated due to their essential function in eukaryotic genome regulation. Histone modifications have been effectively studied using modified bottom-up proteomics approaches; however, the methods often do not capture single-molecule combinations of PTMs (proteoforms) that mediate known and expected biochemical mechanisms. Both middle-down mass spectrometry (MS) and top-down MS quantitation of H4 proteoforms present viable access to this important information. Histone H4 middle-down has previously avoided GluC digestion due to complex digestion products and interferences; however, the common AspN digestion cleaves at amino acid 23, disconnecting K31ac from other PTMs. Here, we demonstrate the effective use of GluC-based middle-down quantitation and compare it to top-down-based quantitation of proteoforms. Despite potential interferences in the m/z space, the proteoforms arising from all three GluC products (E52, E53, and E63) and intact H4 are chromatographically resolved and successfully analyzed in a single LC–MS analysis. Quantitative results and associated analytical metrics are compared between the different analytes of a single sample digested to different extents to reveal general concordance as well as the relative biases and complementarity of each approach. There is moderate proteoform discordance between digestion products (e.g., E52 and E53); however, each digestion product exhibits high concordance, regardless of digestion time. Under the conditions used, the GluC products are better chromatographically resolved yet show greater variance than the top-down quantitation that are more extensively sampled for MS2. GluC-based middle-down of H4 is thus viable. Both top-down and middle-down approaches have comparable quantitation capacity and are complementary.

Abstract Simultaneous enrichment of glyco- and phosphopeptides will benefit the studies of biological processes regulated by these posttranslational modifications (PTMs). It will also reveal potential crosstalk between these two ubiquitous PTMs. Unlike custom-designed multifunctional solid phase extraction (SPE) materials, operating strong anion exchange (SAX) resin in electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) mode provides a readily available strategy to analytical labs for enrichment of these PTMs for subsequent mass spectrometry (MS)-based characterization. However, the choice of mobile phase has largely relied on empirical rules from hydrophilic interaction chromatography (HILIC) or ion-exchange chromatography (IEX) without further optimization and adjustments. In this study, ten mobile phase compositions of ERLIC were systematically compared; the impact of multiple factors including organic phase proportion, ion pairing reagent, pH, and salt on the retention of glycosylated and phosphorylated peptides was evaluated. This study demonstrated good enrichment of glyco- and phosphopeptides from the nonmodified peptides in a complex tryptic digest. Moreover, the enriched glyco- and phosphopeptides elute in different fractions by orthogonal retention mechanisms of hydrophilic interaction and electrostatic interaction in ERLIC, maximizing the LC-MS identification of each PTM. The optimized mobile phase can be adapted to the ERLIC HPLC system, where the high resolution in separating multiple PTMs will benefit large-scale MS-based PTM profiling and in-depth characterization.

Abstract Sarcomeric proteins, including myofilament and Z-disk proteins, play critical roles in regulating muscle contractile properties. A variety of isoforms and post-translational modifications (PTMs) of sarcomeric proteins have been shown to be associated with modulation of muscle functions and the occurrence of muscle diseases. Non-human primates (NHPs) are excellent research models for sarcopenia, a disease associated with alterations in sarcomeric proteins, due to their marked similarities to humans. However, the sarcomeric proteins in NHP skeletal muscle have not been well characterized. To gain a deeper understanding of sarcomeric proteins in NHP skeletal muscle, we employed top-down mass spectrometry (MS) to conduct a comprehensive analysis on isoforms and PTMs of sarcomeric proteins in rhesus macaque skeletal muscle. We identified 23 protein isoforms with 46 proteoforms of sarcomeric proteins, including 6 isoforms with 18 proteoforms from fast skeletal troponin T. Particularly, for the first time, a novel PDZ/LIM domain protein isoform, PDLIM7, was characterized with a newly identified protein sequence. Moreover, we also identified multiple PTMs on these proteins, including deamidation, methylation, acetylation, tri-methylation, phosphorylation, and S-glutathionylation. Most PTM sites were localized, including Asn13 deamidation on MLC-2S; His73 methylation on αactin; N-terminal acetylation on most identified proteins; N-terminal tri-methylation on MLC-1S, MLC-1F, MLC-2S, and MLC-2F; Ser14 phosphorylation on MLC-2S; and Ser15 and Ser16 phosphorylation on MLC-2F. In summary, a comprehensive characterization of sarcomeric proteins including multiple isoforms and PTMs in NHP skeletal muscle was achieved by analyzing intact proteins in the top-down MS approach.

Abstract Process analytical technologies (PAT) applied to process monitoring and control generally provide multiple outputs that can come from different sensors or from different model outputs generated from a single multivariate sensor. This paper provides a contribution to current data fusion strategies for the combination of sensor and/or model outputs in the development of multivariate statistical process control (MSPC) models. Data fusion is explored through three real process examples combining output from multivariate models coming from the same sensor uniquely (in the near-infrared (NIR)-based end point detection of a two-stage polyester production process) or the combination of these outputs with other process variable sensors (using NIR-based model outputs and temperature values in the end point detection of a fluidized bed drying process and in the on-line control of a distillation process). The three examples studied show clearly the flexibility in the choice of model outputs (e.g. key properties prediction by multivariate calibration, process profiles issued from a multivariate resolution method) and the benefit of using MSPC models based on fused information including model outputs towards those based on raw single sensor outputs for both process control and diagnostic and interpretation of abnormal process situations. The data fusion strategy proposed is of general applicability for any analytical or bioanalytical process that produces several sensor and/or model outputs. Graphical abstract

Abstract Multi-block glucans comprising permethylated and partially methylated blocks are compounds of interest. In order to monitor their formation by transglycosylation of corresponding starting glucans, a method has been developed and applied to model compounds. This method allows determining the average length of the blocks and the progress of incorporation of methyl blocks in partially methylated sequences with a random distribution. The method, comprising liquid chromatography mass spectrometry (LC-MS) and electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MSn) measurements of two types of peralkylated glucans representing derivatives of the target compounds, is comprehensively described and discussed. ESI-MSn allows looking into the sequences of oligomeric domains. In addition, transglycosylation is followed by attenuated total reflection FTIR and NMR spectroscopy. Graphical abstract

Unfortunately, after online publication, a formatting mistake was found in Table 1 (Chemical structures and MRM transitions used for quantitation). The original article has been corrected.

Abstract Bloodstains found at crime scenes contain immense information about the crime; thus, studies involving analysis of small molecules in bloodstains have been conducted. However, most of these studies have not accounted for the difference in the results of small molecule analysis due to the surface of bloodstains. To evaluate the “surface effect,” we prepared bloodstains on seven surfaces, including both absorbent and non-absorbent surfaces, and performed global small molecule analysis by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). We used three indicators: (1) count recovery rate (%) of molecular features (MFs), (2) the number of MFs extracted from the surface without bloodstains, and (3) difference in abundance recovery rate (%) of MFs, to determine the ranking of the seven surfaces in the order of their similarity with blood. We also confirmed the correlation between each surface and blood through multivariate analysis. We found that the non-absorbent surfaces ranked better than the absorbent surfaces; wooden flooring was ranked as the most efficient surface, followed by stainless, vinyl flooring, glass, tile, filter paper, and mixed cotton. This study will help in the selection of the most efficient surface for collection of bloodstains for small molecule analysis from a crime scene. This is the first study to identify the effects of surface on extraction of global small molecules from bloodstains; it will help forensic scientists in obtaining more accurate information from small molecules present in the bloodstains collected at the field. Graphical abstract

Abstract In this work, the development of a simple, fast and reliable method for the evaluation of a group of twelve plastic migrants in alcoholic and non-alcoholic beverages widely consumed by the population has been carried out. For that, a modified QuEChERS method for the extraction and preconcentration of the target compounds has been used prior to their separation and quantification by gas chromatography coupled to triple quadrupole tandem mass spectrometry. The whole methodology was validated for beer, cider and grape juice matrices, using dibutyl phthalate-3,4,5,6-d4 as surrogate. Recovery ranged from 75 to 120% for all matrices with relative standard deviation values lower than 20%, and the limits of quantification of the method were achieved in the range 0.034–1.415 μg/L. Finally, the analysis of different beer, cider and grape juice samples commercialised in different supermarkets of Tenerife was carried out, finding the presence of four of the evaluated phthalates in the range 0.14–1.1 μg/L in some of the evaluated beers, six of them in several cider samples, in the range 0.3–2.1 μg/L, and one in the range 1.2–1.5 μg/L in three of the analysed grape juices.

Cancer cells’ MMP9 activity plays vital roles in tumor development. Tumor cells are in an adhesion profile during cell-cell and cell-matrix interaction. However, it is challenging for current platforms (e.g., typical droplet systems) to measure MMP9 secreted by single cells in an adhesion profile and retrieve the cells of interest for downstream analysis. Herein, we report a single-cell protease sensor (SCPS) based on ‘virtual droplet’ that can fulfill the above two requirements. SCPS can form 648 virtual droplets within one minute as a one-cell-per-droplet profile, which offers an isolated space with a substrate to support cells’ adhesion and enables MMP9 measurement for hundreds of single adhered cells within two hours. In addition to high cellular heterogeneity of cancer cells in MMP9 production, we also found that adhered MDA-MB-231 cells produced relatively more MMP9 than that done by suspended cells. Furthermore, the cells producing high MMP9 and low MMP9 were retrieved and mRNA-sequence was performed on them. The results demonstrated that some KEGG pathways associated with cell migration and invasion were enriched and a few related genes (e.g., FYN, MAPK3, RAF) were upregulated in high-MMP9 cells. This SCPS system provides a promising strategy for measuring single-cell’s protease activity.

Point-of-care quantitative detection of biochemical markers has broad applications in resource-limited settings. However, current challenges including difficulty in sample preparation and limitation in result quantitation make point-of-care detection platforms failed to achieve fully sample-to-answer detection or meet the clinical quantitative demands. Here, we developed a novel point-of-care platform to realize fully sample-to-answer biochemical marker quantitation in whole blood. Our platform integrated a plasma separation module and a detection module. The plasma separation module contained a plasma separation strip could rapidly separate the plasma from whole blood samples by lateral flow. The detection module generated a colorimetric signal which could be quantified by the smartphone ambient light sensor (ALS) in an equipment-free manner. As a proof-of-concept, two hepatobiliary disease-associated markers, total bilirubin (TBil) and direct bilirubin (DBil), were detected from whole blood to quantitative result. The quantitative performance for clinical samples was highly consistent with the well-established clinical chemistry analyzer. Our platform exhibited remarkable advantages of significant portability (< 40 g), low cost (< $5), rapidity (< 5 min), instrument-free, high sensitivity (< 1 μM), and accuracy (89.5 % for TBil, 94.7 % for DBil), which showed up a great potential for biochemical markers detection in resource-limited settings.

Mode noise suppression in off-axis integrated cavity output spectroscopy (OA-ICOS) is a key for improving the signal-to-noise ratio (SNR) of a sensor system, which basically depends on the ability to smooth out the cavity mode structure and to reduce the cavity mode linewidth. We demonstrated a novel dual-input dual-output (DIDO) coupling scheme of OA-ICOS for mode noise suppression. The influences of beam splitting ratio and light reflection number to the output intensity and cavity mode linewidth were theoretically studied. Experimental investigation on the suppression of cavity mode noise was carried out in terms of detection sensitivity and SNR through methane (CH4) measurements. A SNR of 221 and a detection sensitivity of 1.73 × 10-8 cm-1 Hz-1/2 was obtained for the DIDO-based OA-ICOS sensor system. The SNR was improved by a factor of ∼ 2.5 and the sensitivity was improved by a factor of ∼ 2.2 compared to the regular single-input single-output (R-SISO) approach. Multi-input multi-output (MIMO) configuration was further numerically studied to verify the noise suppression ability of this detection concept. This work reveals a new laser-to-cavity coupling method and provides a novel way to exploit OA-ICOS sensors with improved SNR and sensitivity.

W-doped NiO nanotubes (NTs) were successfully synthesized for efficient sensing of ethanol vapor using a low cost and economical electrospinning method. The response (resistance ratio) of sensor based on 4% W-NiO NTs to100 ppm ethanol is as high as 40.56 at 200 °C, which is 10 times higher than that of pure NiO sensor. This significant enhancement in sensor response can be attributed to the change in morphology, increase in oxygen vacancies, and the decrease in hole concentration in NiO by W doping. Based on the adsorption and desorption theory of oxygen, we also demonstrated that the atmospheric oxygen content can improve the sensor response and shorten the response time by increasing the amount of adsorbed oxygen.

Pure and Ti-doped NiO multiroom spheres were prepared via ultrasonic spray pyrolysis, and their gas sensing characteristics were investigated. The sensor using 10 at% Ti-doped NiO multiroom spheres exhibited an unprecedented high response (resistance ratio = 337.8) to 1 ppm p-xylene at 350 ℃, whereas the sensor using pure NiO multiroom spheres exhibited a negligibly low response (1.3). Moreover, the control of the Ti doping and film thickness provided intriguing strategies for tuning the xylene and methylbenzene sensing characteristics, such as the selectivity, response, sensitivity (slope between response and gas concentration), and detection limit. The versatile tunability on gas sensing characteristics was explained by the Ti-doping-induced variation of the oxygen adsorption, mesoporosity, specific surface area, and charge-carrier concentration, as well as the control over the reforming and oxidation of the analyte gases using the multiroom-structured micro-reactors with high catalytic activity.

In this study, we developed a simple and sensitive surface-enhanced Raman scattering (SERS) technique for the detection of choline in infant formulas based on a filter-based flexible substrate. The flexible substrate with excellent SERS activity and reproducibility was fabricated using a syringe filter and Ag triangular nanoplates. The Raman marker, 3-mercaptophenylboronic acid, was oxidised to 3-hydroxythiophenol in the presence of H2O2, which caused a decrease in the SERS peak intensity ratio (I1021 cm-1: I996 cm-1). Utilising the enhanced flexible substrate, a quantitative detection method for H2O2 was developed. Additionally, choline could be hydrolysed by choline oxidase to generate betaine and H2O2. Thus, the SERS method was successfully applied to detect choline in the concentration range of 10-3–10-7 M with a beneficial limit of detection as low as 8.36 nM. Importantly, the recovery of choline from infant formula milk powder was approximately 99%. The excellent performance of the flexible substrate-based SERS method demonstrated its potential for application in H2O2-generated oxidase-based biosensing.

In this study we report for the first time on a surface acoustic wave (SAW) sensor modified with a molecularly imprinted polymer (MIP) selectively recognizing the cerebral dopamine neurotrophic factor (CDNF) protein. CDNF-MIP as a synthetic recognition element was prepared by a simple electrochemical surface imprinting approach allowing its reliable interfacing with SAW sensor. The optimal thickness of the MIP layer as well as a suitable pretreatment method were adjusted in order to improve the recognition capacity and selectivity of the resulting CDNF-MIP sensor. The selectivity of the sensor was studied by the carefully designed competitive binding experiments, which revealed that the sensor can sense CNDF confidently in label-free manner starting from 0.1 pg/ml. We anticipate that the findings can be a premise for fabrication of cost-effective research or diagnostics tools in the field of neurodegenerative diseases.