Analyte Capture Research Articles

Adapting standardized trout monitoring to a changing climate for the upper Yellowstone River, Montana, USA

AbstractObjectiveLong‐term standardized monitoring programs are fundamental to assessing how fish populations respond to anthropogenic stressors. Standardized monitoring programs may need to adopt new methods to adapt to rapid environmental changes that are associated with a changing climate. In the upper Yellowstone River, Montana, biologists have used a standardized, mark–recapture monitoring protocol to annually estimate the abundance of trout since 1978 to assess population status and trends. However, within the past two decades, climate change has caused changes in discharge timing that have prevented standardized monitoring from occurring annually.MethodsWe investigated the feasibility of using two analytical methods, N‐mixture models and mean capture probability, for estimating the abundance of three trout species in the upper Yellowstone River using the historical long‐term data set; these methods allow abundance to be estimated when a mark–recapture estimate cannot be obtained due to hydrologic conditions.ResultWhen compared with abundance estimates from mark–recapture methods, N‐mixture models most often resulted in negatively biased abundance estimates, whereas mean capture probability analyses resulted in positively biased abundance estimates. Additionally, N‐mixture models produced negatively biased estimates when tested against true abundance values from simulated data sets. The bias in the N‐mixture model estimates was caused by poor model fit and variation in capture probability. The bias in the mean capture probability estimates was caused by heterogeneity in capture probability, likely caused by variable environmental conditions, which were not accounted for in the models.ConclusionN‐mixture models and mean capture probability are not viable alternatives for estimating abundance in the upper Yellowstone River. Thus, exploring additional adaptations to sampling methodologies and analytical approaches, including models that require individually marked fish, will be valuable for this system. Climate change will undoubtedly necessitate changes to standardized sampling methods throughout the world; thus, developing alternative sampling and analytical methods will be important for maintaining the utility of long‐term data sets.

4-Vinylpyridine copolymers for improved LC–MS tryptophan and kynurenine determination in human serum

Tryptophan (an essential amino acid) and its clinically important metabolite—kynurenine contribute to several fundamental biological processes and methods that allow their determination in biological samples are in demand. The novelty of the work was a demonstration of the utility of two polymers: 4-vinylpyridine crosslinked with trimethylolpropane trimethacrylate (poly(4VP-co-TRIM)) or 1,4-dimethacryloyloxybenzene (poly(4VP-co-14DMB))—in terms of human serum clean-up for simultaneous LC–MS determination of tryptophan and kynurenine. The goal was to achieve a reduction of the matrix effect, which is responsible for signal suppression, with minimal capture of analytes. The adsorption properties of the polymeric beads were studied by evaluating the adsorption kinetics and isotherms in model matrices. Therefore, the adsorption capacities of both molecules were not efficient, the tested 4-vinylpyridine-based copolymers have shown great promise (especially poly(4VP-co-TRIM)) as sorbents for serum clean-up. In the model human serum matrix, poly(4VP-co-TRIM) provided good recoveries of tryptophan and kynurenine (76% and 87%, respectively) and allowed for the reduction of the matrix effect. Performances of both copolymers were compared to those of commercially available sorbents (octadecylsilane, activated charcoal, and primary secondary amine).

Molecularly Imprinted Polymer Modified Laser-Engraved Graphene Electrode for the Ultra-Sensitive and Specific Detection of Ascorbic Acid

Sensitive and accurate detection of small molecule targets is critical for a variety of applications, including environmental monitoring, food safety and medical diagnostics. Electrochemical sensors with the advantages of high sensitivity, accuracy, convenience and low-cost make them well suited for these applications. Moreover, the combination of electrochemical sensors with micro-and nanofabrication technology offers the possibility of integrated and intelligent sensing systems.Figure 1. (a) The SEM characterization of PPD/LEG electrode, (b) the FT-IR of LEG and PPD/LEG electrode, (c) the Nyquist plots of LEG and PPD/LEG electrode, (d) the specificity, (e) linear relationship and (f) sensitivity of integrated electrochemical microsensor.In general, the ultimate performance of an electrochemical sensor relies on the high efficiency of bio/chemical reactions as well as transport of the analytes by diffusion onto the electrode. Accordingly, the desired electrode materials should permit very fast mass transport rates and possess the capability of specific capture of target analytes. Laser-etched graphene (LEG) electrodes featured with the advantages of porous three-dimensional network structure, large specific surface area, and high conductivity, are considered as an ideal sensing element for sensitive molecules detection, but cannot recognize specific targets. Molecularly imprinted polymers (MIPs) are low-cost and easy to modify on electrochemical sensing surfaces. It can be used to form molecular recognition sites by synthesizing target templates in polymers, giving the modified electrodes the ability to specifically recognize target molecules, which is an ideal modification material for electrochemical sensor platforms.Herein, we propose an integrated electrochemical microsensor sensing ultra-low concentration of ascorbic acid (AA) molecules by using MIP modified LEG as electrode material. The main characteristics of the detection system are as follows: 1) LEG electrode enables electrochemical sensing strategy with simple preparation and high sensitivity, 2) MIP poly-o-phenylenediamine (PPD) membrane on the surface of graphene provides the desirable property for highly selective AA molecular recognition, 3) the integrated PPD/LEG electrode allows to detect AA molecules in a ultra-low concentration range which is superior than that of other electrochemical detection techniques.The surface morphology of PPD/LEG electrode is characterized by using scanning electron microscopy (SEM, shown in Figure 1a), from which LEG shows three-dimensional network porous structure and the nature of graphene. In addition, the electropolymerized PPD membrane exhibits a rough and porous surface which would provide the large surface area for the adsorption of target AA molecules at the modified electrode. The formation of PPD/LEG electrode is further examined by Fourier Transform Infrared Spectroscopy (FT-IR Spectrometer) in Figure 1b. The polymerization of PPD membrane on the surface of the LEG electrode is confirmed by the appearance of two absorption peaks at 3385 cm-1 and 3360 cm-1, which are related to the stretching vibration of the -NH2 from the PPD. As shown in the Nyquist plots (Figure 1c), the semicircle in the high-frequency region is described as an intrinsic electron-transfer resistance in the electrode materials. The identical semicircles at high-frequency region of two electrodes indicate nearly equal electron transfer resistance (Rct) of LEG and PPD/LEG. The low-frequency region of the Nyquist plot is described as surface diffusion control, and the increase in the linear slope represents an enhanced surface diffusion control process at the electrodes demonstrating the lower impedance of the PPD/LEG electrode. Figure 1d verifies the specific recognition of AA molecules by the PPD/LEG electrode in PBS mixed with 1 mM of AA, dopamine (DA), uric acid (UA) and acetaminophen (AP) molecules. It can be seen that compared with the LEG electrode, the DPV response of the PPD/LEG electrode to DA, UA and AP molecules is significantly reduced, while the response to AA molecules is significantly enhanced. Furthermore, the ability of the integrated electrochemical microsensor to detect ultra-low concentrations of AA molecules in the 10 nM to 100 nM range is shown in Figure 1e, with a LOD of 2 nM (Figure 1f).In conclusion, we present an integrated electrochemical microsensor that can specifically detect AA molecules with ultra-high sensitivity. The LEG electrode with the modification of PPD membrane can effectively realize the specific recognition and accurate detection of AA molecules in mixed solutions. This integrated electrochemical sensing method is expected to be applied to the selective detection of multiple small molecule targets in complex environments.Key words: Laser-engraved Graphene Electrodes, Molecularly Imprinted Polymers, Integrated Electrochemical Microsensor, Ultra Sensitivity Detection. Figure 1

Three-dimensional multi-constraint analytical capture zone against maneuvering targets with velocity advantages

Concerning the capture problem against arbitrary maneuvering targets, whose overload is high maneuvering but upper bounded and velocity has advantages, this paper elucidates a three-dimensional multi-constraint analytical capture zone, exhibiting prominent guiding significance to the initial states of the terminal guidance. Unlike most existing capture zone studies, which are represented by initial relative velocity, the proposed capture zone investigates the initial velocity heading angle and side-window angle. First, the asymptotic fast convergence anti-interference guidance law is presented via motion camouflage theory, and it meets the Field of View (FOV) constraint by theoretical analysis. On this basis, the capture zone is derived with overload limits based on the Lyapunov-based function. Then, it is converted to the form defined by the velocity heading and side-window angles, considering the FOV constraint. Finally, the sensitivity of the capture zone to the designed guidance algorithm’s different influencing factors and the gain boundary are deduced and analyzed to provide a theoretical basis for augmenting the analytical capture zone during a practical engagement. The findings reveal the capture zone correlation mechanism of terminal guidance law and give academic support to the subsequent acquisition of arbitrary maneuvering targets, which has potential application value.

Understanding Electrophoresis and Electroosmosis in Nanopore Sensing with the Help of the Nanopore Electro-Osmotic Trap.

Nanopore technology is widely used for sequencing DNA, RNA, and peptides with single-molecule resolution, for fingerprinting single proteins, and for detecting metabolites. However, the molecular driving forces controlling the analyte capture, its residence time, and its escape have remained incompletely understood. The recently developed Nanopore Electro-Osmotic trap (NEOtrap) is well fit to study these basic physical processes in nanopore sensing, as it reveals previously missed events. Here, we use the NEOtrap to quantitate the electro-osmotic and electrophoretic forces that act on proteins inside the nanopore. We establish a physical model to describe the capture and escape processes, including the trapping energy potential. We verified the model with experimental data on CRISPR dCas9-RNA-DNA complexes, where we systematically screened crucial modeling parameters such as the size and net charge of the complex. Tuning the balance between electrophoretic and electro-osmotic forces in this way, we compare the trends in the kinetic parameters with our theoretical models. The result is a comprehensive picture of the major physical processes in nanopore trapping, which helps to guide the experiment design and signal interpretation in nanopore experiments.

Revolutionizing biomarker analysis one tip at a time—Coupling antibody to Volumetric Absorptive Microsamplers for sensitive LC-MS analysis

The constant pursuit of efficient and cost-effective methods for analyzing human samples drives ongoing innovation in biomedical research. Introduced in 2014, Volumetric Absorptive Microsampling (VAMS) technology ensures fixed blood volume absorption and enhanced sample uniformity. Our study aims to enhance VAMS functionality by integrating sample preparation onto the device primarily used for sample collection. This involves the adsorption of antibodies onto VAMS tips, enabling instant sample clean-up at the time of sample collection. Using human chorionic gonadotropin (hCG) as a model analyte, we evaluated the qualitative and quantitative performance of Affinity-VAMS. First, we showed that adsorbing and covalently binding monoclonal antibodies to VAMS tips results in capturing of the target analyte in comparison to unmodified VAMS. Due to the ease of preparation, we moved forward using antibody adsorption to VAMS tip and optimized the procedure. Optimization of the procedure involved fine-tuning the antibody coupling step, washing process, and determining the optimal amount of antibody required, leading to a streamlined process with significant time savings up to two days. Recovery experiments demonstrate successful capture of the target analyte by the Affinity-VAMS, while matrix effects and stability assessments indicate no negative effects from serum matrix or storage conditions. Finally, quantitative analysis shows promising performance of the Affinity-VAMS in detecting different concentrations of the target analyte in the concentration range between 7.5 - 25 ng·mL−1. The calculated correlation factor was R2 of 0.9988 and limit of detection 2.5 ng·mL−1. The precision lays within the ICH guidelines for bioanalytical method validation. While this report is focused on the proof of concept of the Affinity-VAMS, our findings demonstrate the potential for the usage of modified VAMS in remote sampling and integrated sample processing, enhancing biomarker analysis in clinical and research settings.

Improved solution-based SERS detection of creatinine by inducing hydrogen-bonding interaction for effective analyte capture

Recently, solution-based surface-enhanced Raman scattering (SERS) detection technique has been widely recognized due to its cost-effectiveness, simplicity, and ease of use. However, solution-based SERS is limited for practical applications mainly because of the weak adsorption affinity of the target biomolecules to the surface of plasmonic nanoparticles. Herein, we developed a highly sensitive solution-based SERS sensing platform based on mercaptopropionic acid (MPA)-capped silver-coated gold nanostars (SGNS@MPA), which allows efficient enrichment on the nanostars surface for improved detection of an analyte: creatinine, a potential biomarker of chronic kidney disease (CKD). The SGNS@MPA exhibited high enrichment ability towards creatinine molecules in alkaline medium (pH-9) through multiple hydrogen bonding interaction, which causes aggregation of the nanoparticles and enhances the SERS signal of creatinine. The detection limit for creatinine was achieved at 0.1 nM, with a limit of detection (LOD) value of 14.6 pM. As a proof-of-concept demonstration, we conducted the first quantitative detection of creatinine in noninvasive human fluids, such as saliva and sweat, under separation-free conditions. We achieved a detection limit of up to 1 nM for both saliva and sweat, with LOD values as low as 0.136 nM for saliva and 0.266 nM for sweat. Overall, our molecular enrichment strategy offers a new way to improve the solution-based SERS detection technique for real-world practical applications in point-of-care settings and low-resource settings.

Sandwich Immuno-RCA Assay with Single Molecule Counting Readout: The Importance of Biointerface Design.

The analysis of low-abundance protein molecules in human serum is reported based on counting of the individual affinity-captured analyte on a solid sensor surface, yielding a readout format similar to digital assays. In this approach, a sandwich immunoassay with rolling circle amplification (RCA) is used for single molecule detection (SMD) through associating the target analyte with spatially distinct bright spots observed by fluorescence microscopy. The unspecific interaction of the target analyte and other immunoassay constituents with the sensor surface is of particular interest in this work, as it ultimately limits the performance of this assay. It is minimized by the design of the respective biointerface and thiol self-assembled monolayer with oligoethylene (OEG) head groups, and a poly[oligo(ethylene glycol) methacrylate] (pHOEGMA) antifouling polymer brush was used for the immobilization of the capture antibody (cAb) on the sensor surface. The assay relying on fluorescent postlabeling of long single-stranded DNA that are grafted from the detection antibody (dAb) by RCA was established with the help of combined surface plasmon resonance and surface plasmon-enhanced fluorescence monitoring of reaction kinetics. These techniques were employed for in situ measurements of conjugating of cAb to the sensor surface, tagging of short single-stranded DNA to dAb, affinity capture of the target analyte from the analyzed liquid sample, and the fluorescence readout of the RCA product. Through mitigation of adsorption of nontarget molecules on the sensor surface by tailoring of the antifouling biointerface, optimizing conjugation chemistry, and by implementing weak Coulombic repelling between dAb and the sensor surface, the limit of detection (LOD) of the assay was substantially improved. For the chosen interleukin-6 biomarker, SMD assay with LOD at a concentration of 4.3 fM was achieved for model (spiked) samples, and validation of the ability of detection of standard human serum samples is demonstrated.

Surface Modification of Polystyrene with Boronic Acid for Immunoaffinity-Based Cell Enrichment.

Obtaining an enriched and phenotypically pure cell population from heterogeneous cell mixtures is important for diagnostics and biosensing. Existing techniques such as fluorescent-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) require preincubation with antibodies (Ab) and specialized equipment. Cell immunopanning removes the need for preincubation and can be done with no specialized equipment. The majority of the available antibody-mediated analyte capture techniques require a modification to the Abs for binding. In this work, no antibody modification is used because we take advantage of the carbohydrate chain in the Fc region of Ab. We use boronic acid as a cross-linker to bind the Ab to a modified surface. The process allows for functional orientation and cleavable binding of the Ab. In this study, we created an immunoaffinity matrix on polystyrene (PS), an inexpensive and ubiquitous plastic. We observed a 37% increase in Ab binding compared with that of a passive adsorption approach. The method also displayed a more consistent antibody binding with 17 times less variation in Ab loading among replicates than did the passive adsorption approach. Surface topography analysis revealed that a dextran coating reduced nonspecific antibody binding. Elemental analysis (XPS) was used to characterize the surface at different stages and showed that APBA molecules can bind upside-down on the surface. While upside-down antibodies likely remain functional, their elution behavior might differ from those bound in the desired way. Cell capture experiments show that the new surface has 43% better selectivity and 2.4-fold higher capture efficiency compared to a control surface of passively adsorbed Abs. This specific surface chemistry modification will allow the targeted capture of cells or analytes with the option of chemical detachment for further research and characterization.

DIGITISING SENSITIVE HERITAGE MONUMENTS IN ANTARCTICA

Abstract. During the Antarctica expedition CHAQ2020, several cultural heritage sites – remains from the Swedish South Polar Expedition (1901–1903) – were documented using a range of different techniques and technologies. These physical monuments and environments are for all intents and purposes unavailable for most researchers due to their remote location and are also threatened by the effects of climate change. Hence, the deployed documentation techniques and technologies were selected both as a consequence of the inherently difficult conditions in Antarctica, where their reliance, durability, and speed were key considerations, but also for their perceived ability to document the unique and fragile environment. The documentation was carried out with the double intention of both allowing for observations in situ through processes of analytical drawings and data capture, but also capturing the environment as broadly and deeply as possible, in essence making a copy of it open for studies of unknown unknowns, that could serve as a source material for research questions still undefined. Hence, with the documentation of the winter station on Snow Hill Island as a case study, and with a perspective on documentation as a method through which to process, preserve, and disseminate information, this article serves to critically detail, compare, and evaluate the digital techniques and technologies that the expedition deployed to capture architectural elements and spatial contexts, and the data that could be obtained through these.

Triple multivalent aptamers within DNA tetrahedron on reduced graphene oxide electrode: Unlocking enhanced sensitivity and accelerated reactions in electrochemical sensing

DNA nanostructures are emerging as promising biosensing platforms due to their programmability, predictable assembly, and compatibility with aptamers for enhanced selectivity. This study focuses on a triple-multivalent aptamer (tApt) complex immobilized on a tetrahedral DNA nanostructure (TDN) and integrated with an electrochemically reduced graphene oxide (ERGO) electrode for highly sensitive mercury ion (Hg2+) detection. Compared to a linear multivalent aptamer-modified electrode (S2/ERGO-GCE), the 3D tApt/ERGO-GCE aptasensor exhibits superior sensitivity, signal amplification, and reaction kinetics. The tApt/ERGO-GCE sensor achieves an exceptional limit of detection (LOD) of 4.1 zM, surpassing the LOD of 0.71 fM for S2/ERGO-GCE. Additionally, the tApt/ERGO-GCE sensor demonstrates faster response times, with a half-saturation time (T1/2) of 6 minutes compared to 17 minutes for S2/ERGO/GCE. The 3D tApt aptamer's superior performance is attributed to its tetrahedral DNA structure integrated on ERGO, providing multiple aptamer binding sites, facilitating oriented immobilization on the electrode surface, and enhancing analyte capture and concentration. In contrast, the linear S2 aptamers lack rigidity, resulting in a disordered orientation on the electrode surface, hindering efficient Hg2+ binding and reducing target molecule binding efficiency. This study underscores the potential of triple-multivalent aptamer-based nanostructures for ultrasensitive and rapid biosensing applications. The tApt/ERGO-GCE aptasensor's exceptional sensitivity, signal amplification, and reaction kinetics make it a promising tool for Hg2+ detection and other biosensing applications.

An ultrasensitive 4-aminophenol electrochemical sensors based on zinc and nitrogen-doped γ-cyclodextrin composites

4-Aminophenol (4-AP) is an environmental pollutant that is harmful to aquatic organisms and can cause long-term adverse effects in the aquatic environment. Herein, a Zn,N-γ-CD/GCE sensing platform was constructed by utilizing the complexation of Zn ions with γ-cyclodextrin (γ-CD), along with the composite of N-doped γ-cyclodextrin (N-γ-CD) and ZnCl2, for the detection of 4-AP. The presence of pore structures and hydrogen bonding groups in N-γ-CD enables effective capture of the target analyte through host–guest interactions, thereby enhancing the detection efficiency. The doping of Zn metal significantly improves the sensitivity of the sensing platform. After optimization, the detection limit of the Zn,N-γ-CD/GCE sensor was as low as 29.1 nM. Moreover, the sensor exhibits reliable repeatability, reproducibility, and stability. The practical feasibility of detecting 4-AP in real samples using this sensor demonstrated a recovery rate of 94.3 %–105.5 %, providing a new method for the accurate detection of 4-AP.

Lithographically defined encoded magnetic heterostructures for the targeted screening of kidney cancer.

Renal cell carcinoma (RCC) is the 7th commonest cancer in the UK and the most lethal urological malignancy; 50% of all RCC patients will die from the condition. However, if identified early enough, small RCCs are usually cured by surgery or percutaneous procedures, with 95% 10 year survival. This study describes a newly developed non-invasive urine-based assay for the early detection of RCC. Our approach uses encoded magnetically controllable heterostructures as a substrate for immunoassays. These heterostructures have molecular recognition abilities and embedded patterned codes for a rapid identification of RCC biomarkers. The magnetic heterostructures developed for this study have a magnetic configuration designed for a remote multi axial control of their orientation by external magnetic fields, this control facilitates the code readout when the heterostructures are in liquid. Furthermore, the optical encoding of each set of heterostructures provides a multiplexed analyte capture platform, as different sets of heterostructures, specific to different biomarkers can be mixed together in a patient sample. Our results show a precise magnetic control of the heterostructures with an efficient code readout during liquid immunoassays. The use of functionalised magnetic heterostructures as a substrate for immunoassay is validated for urine specimen spiked with recombinant RCC biomarkers. Initial results of the newly proposed screening method on urine samples from RCC patients, and controls with no renal disorders are presented in this study. Comprehensive optimisation cycles are in progress to validate the robustness of this technology as a novel, non-invasive screening method for RCC.

Cancer Marker Immunosensing through Surface-Enhanced Photoluminescence on Nanostructured Silver Substrates.

Nanostructured noble metal surfaces enhance the photoluminescence emitted by fluorescent molecules, permitting the development of highly sensitive fluorescence immunoassays. To this end, surfaces with silicon nanowires decorated with silver nanoparticles in the form of dendrites or aggregates were evaluated as substrates for the immunochemical detection of two ovarian cancer indicators, carbohydrate antigen 125 (CA125) and human epididymis protein 4 (HE4). The substrates were prepared by metal-enhanced chemical etching of silicon wafers to create, in one step, silicon nanowires and silver nanoparticles on top of them. For both analytes, non-competitive immunoassays were developed using pairs of highly specific monoclonal antibodies, one for analyte capture on the substrate and the other for detection. In order to facilitate the identification of the immunocomplexes through a reaction with streptavidin labeled with Rhodamine Red-X, the detection antibodies were biotinylated. An in-house-developed optical set-up was used for photoluminescence signal measurements after assay completion. The detection limits achieved were 2.5 U/mL and 3.12 pM for CA125 and HE4, respectively, with linear dynamic ranges extending up to 500 U/mL for CA125 and up to 500 pM for HE4, covering the concentration ranges of both healthy and ovarian cancer patients. Thus, the proposed method could be implemented for the early diagnosis and/or prognosis and monitoring of ovarian cancer.

Methodologies for Spontaneous Preparation of Chemosensors and Their Arrays Using Off‐the‐Shelf Reagents

AbstractChemosensors offer promising candidates for visualizing molecular recognition information through colorimetric or fluorescence responses. When designing chemosensors, the following requirements should be considered: 1) molecular geometries of the analytes, 2) mechanisms that cause optical changes upon analyte capture, and 3) solubility for sensing applications. However, the designs and realization of chemosensors that meet these requirements remains a cutting‐edge challenge. Conventional strategies mainly consider the molecular geometries of the receptors and analytes. However, this approach presents the issues related to the extensive synthetic efforts required to obtain elaborate chemosensor designs, leading to decreased water solubility in chemosensors derived from complicated and aromatic molecular structures. This review summarizes the methodologies for self‐assembled chemosensors that use only off‐the‐shelf reagents, to easily obtain various chemosensors without organic synthesis. The self‐assembled chemosensors, comprising off‐the‐shelf reagents with water solubility, facilitates both easy tuning of optical sensing properties and chemical sensing in real samples. The usability of off‐the‐shelf reagents in analytical chemistry will be clarified through comprehensive sensing applications involving simple self‐assembled chemosensors and their arrays.

Radial flow enhances QCM biosensor sensitivity

QCM biosensors are widely used for the detection of a variety of pathogenic microorganisms, and there remains a need for further increases in sensitivity. The majority of QCM biosensors are operated under diffusion-limited conditions that, when used with a standard flow cell, lead to the majority of analyte being captured onto regions of the crystal surface that have limited to no mass sensitivity. Here we show that simple changes to a flow cell architecture (reduction of flow cell height) can provide increases in sensing signal. Furthermore, we show that the use of radial flow will lead to analyte capture directly in the sensitive region of a crystal, thus providing dramatic increases in the biosensor’s sensitivity. We examine this problem from both a theoretical and numerical perspective and present a new method by which to consider how changes to a sensing assay will affect sensor sensitivity. We demonstrate this experimentally through the detection of E. coli using one commercial and two custom-built flow cells having large differences in height, one of which has radial flow. We show that simple reduction in flow cell height using a standard flow cell leads to a 2.4 × in sensitivity, where the further inclusion of radial flow leads to a 5.1 × increase. We further show that these performance increases are only slightly offset by changes in the sensing noise, which were seen to vary slightly when using different flow cells. These results are directly applicable to nearly every QCM biosensor operated using affinity-based detection.

Sterically Enhanced Control of Enzyme-Assisted DNA Assembly.

Traditional methods for the assembly of functionalised DNA structures, involving enzyme restriction and modification, present difficulties when working with small DNA fragments (<100 bp), in part due to a lack of control over enzymatic action during the DNA modification process. This limits the design flexibility and range of accessible DNA structures. Here, we show that these limitations can be overcome by introducing chemical modifications into the DNA that spatially restrict enzymatic activity. This approach, sterically controlled nuclease enhanced (SCoNE) DNA assembly, thereby circumvents the size limitations of conventional Gibson assembly (GA) and allows the preparation of well-defined, functionalised DNA structures with multiple probes for specific analytes, such as IL-6, procalcitonin (PCT), and a biotin reporter group. Notably, when using the same starting materials, conventional GA under typical conditions fails. We demonstrate successful analyte capture based on standard and modified sandwich ELISA and also show how the inclusion of biotin probes provides additional functionality for product isolation.

Plasmonic Dodecahedral-Walled Elongated Nanoframes for Surface-Enhanced Raman Spectroscopy.

Here, elongated pseudohollow nanoframes composed of four rectangular plates enclosing the sides and two open-frame ends with four ridges pointing at the tips for near-field focusing are reported. The side facets act as light-collecting domains and transfer the collected light to the sharp tips for near-field focusing. The nanoframes are hollow inside, allowing the gaseous analyte to penetrate through the entire architecture and enabling efficient detection of gaseous analytes when combined with Raman spectroscopy. The resulting nanostructures are named Au dodecahedral-walled nanoframes. Synthesis of the nanoframes involves shape transformation of Au nanorods with round tips to produce Au-elongated dodecahedra, followed by facet-selective Pt growth, etching of the inner Au, and regrowth steps. The close-packed assembly of Au dodecahedral-walled nanoframes exhibits an attomolar limit of detection toward benzenethiol. This significant enhancement in SERS is attributed to the presence of a flat solid terrace for a large surface area, sharp edges and vertices for strong electromagnetic near-field collection, and open frames for effective analyte transport and capture. Moreover, nanoframes are applied to detect chemical warfare agents, specifically mustard gas simulants, and 20 times higher sensitivity is achieved compared to their solid counterparts.

Construction of High-Active SERS Cavities in a TiO2 Nanochannels-Based Membrane: A Selective Device for Identifying Volatile Aldehyde Biomarkers.

The accurate, sensitive, and selective on-site screening of volatile aldehyde biomarkers for lung cancer is of utmost significance for preclinical cancer diagnosis and treatment. Applying surface-enhanced Raman scattering (SERS) for gas sensing remains difficult due to the small Raman cross section of most gaseous molecules and interference from other components in exhaled breath. Using an Au asymmetrically coated TiO2 nanochannel membrane (Au/TiO2 NM) as the substrate, a ZIF-8-covered Au/TiO2 NM SERS sensing substrate is designed for the detection of exhaled volatile organic compounds (VOCs). Au/TiO2 NM provides uniformly amplified Raman signals for trace measurements in this design. Importantly, the interfacial nanocavities between Au nanoparticles (NPs) and metal-organic frameworks (MOFs) served as gaseous confinement cavities, which is the key to enhancing the capture and adsorption ability toward gaseous analytes. Both ends of the membrane are left open, allowing gas molecules to pass through. This facilitates the diffusion of gaseous molecules and efficient capture of the target analyte. Using benzaldehyde as a typical gas marker model of lung cancer, the Schiff base reaction with a Raman-active probe molecule 4-aminothiophene (4-ATP) pregrafted on Au NPs enabled trace and multicomponent detection. Moreover, the combination of machine learning (ML) and Raman spectroscopy eliminates subjective assessments of gaseous aldehyde species with the use of a single feature peak, allowing for more accurate identification. This membrane sensing device offers a promising design for the development of a desktop SERS analysis system for lung cancer point-of-care testing (POCT).

High‐Density Plasmonic Nanopores for DNA Sensing at Ultra‐Low Concentrations by Plasmon‐Enhanced Raman Spectroscopy

AbstractSolid‐state nanopores are implemented in new and promising platforms that are capable of sensing fundamental biomolecular constituents at the single‐molecule level. However, several limitations and drawbacks remain. For example, the current strategies based on both electrical and optical sensing suffer from low analyte capture rates and challenging nanofabrication procedures. In addition, their limited discrimination power hinders their application in the detection of complex molecular constructs. In contrast, Raman spectroscopy has recently demonstrated the ability to discriminate both nucleotides and amino acids. Herein, a plasmonic nanoassembly is proposed supporting nanopores at high density, in the order of 100 pores per µm2. These findings demonstrate that the device has a high capture rate in the range of a few fm. The pore size is ≈10 nm in diameter and provides an amplification of the electromagnetic field exceeding 103 in intensity at 785 nm. Owing to these features, single‐molecule detection is achieved by means of surface‐enhanced Raman scattering from a solution containing 50 fm DNA molecules (≈4.4 kilobase pairs). Notably, the reported spectra show an average number of 2.5 Raman counts per nucleotide. From this perspective, this number is not far from what is necessary to discriminate the DNA sequence.