Electrokinetic Preconcentration Research Articles

Electrokinetic Preconcentration and Label-Free Electrical Detection of SARS-CoV-2 RNA at a Packed Bed of Bioconjugated Microspheres.

In this communication, we demonstrate the electrical detection of SARS-CoV-2 RNA at low femtomolar concentrations without labels or amplification reactions. Following its extraction from virus particles, the viral RNA was electrokinetically preconcentrated (100-fold) within a packed bed of probe-modified microbeads. This preconcentration was accomplished by counter-flow focusing of the RNA along an electric field gradient generated by faradaic ion concentration polarization (fICP). Hybridization of the 30 kb target RNA to the probe-modified beads sufficiently altered their surface charge to yield a measurable change in the ionic conductivity of the packed bed─a feature leveraged for electrical detection. When a single-stranded DNA probe was used, the sensitivity of this enrichment and sensing scheme was low picomolar. However, the utilization of an uncharged PNA probe improved the limit of detection to 3.4 × 106 viral copies/mL (22.5 fM SARS-CoV-2 RNA). These results are significant for three reasons. First, the sensitivity is remarkable, given the micrometer scale of both the beads and interstitial spaces. Additional gains in enrichment and sensitivity are anticipated as fundamental parametric studies and optimization are undertaken. Second, this study reveals the impact of the probe type on the sensitivity of microscale surface ion conduction (μSIC) sensors. Third, the RNA sensing approach has practical advantages including its utilization of off-the-shelf beads, a reagent-free approach, nonoptical readout, and low driving voltage, which render it amenable to point-of-care (POC) implementation.

Investigation of on-line electrokinetic enrichment strategies for capillary electrophoresis of extracellular vesicles

This work explores strategies for electrokinetic preconcentration of extracellular vesicles (EVs) that are potential source of biomarkers for different diseases. The first approach that led to successful preconcentration of EVs is based on large volume sample stacking (LVSS), allowing an enrichment factor of 7 for CE of EVs with long-end injection (using a capillary with an effective length of 50 cm). Attempts were also made to perform multiple cycles of LVSS, field amplified sample stacking (FASS) and field amplified sample injection (FASI), to improve EVs preconcentration performance. The focus was then put on development of capillary isotachophoresis under high ionic strengths (IS) for electrokinetic enrichment of slow migrating EVs having heterogeneous mobilities. This approach relies on the use of extremely high concentrations of the terminating electrolyte (TE) to slow down the mobility of TE co-ions, rendering them slower than those of EVs. The limit of detection for intact EVs using the developed ITP-UV method reached 8.3 × 108 EVs/mL, allowing an enrichment of 25 folds and a linear calibration up to 4 × 1010 EVs/mL. The ITP-UV and ITP-LIF approaches were applied to provide the electrokinetic signature of EVs of bovine milk and human plasma as well as to visualize more specifically intravesicular fluorescently labelled EVs. The investigation of these strategies shredded light into the challenges still encountered with electrokinetic preconcentration and separation of heterogeneous EVs sub-populations which are discussed herein based on our results and other attempts reported in the literature.

On-Chip Electrochemical Sensing with an Enhanced Detecting Signal Due to Concentration Polarization-Based Analyte Preconcentration.

Here, we integrated two key technologies within a microfluidic system, an electrokinetic preconcentration of analytes by ion Concentration Polarization (CP) and local electrochemical sensors to detect the analytes, which can synergistically act to significantly enhance the detection signal. This synergistic combination, offering both decoupled and coupled operation modes for continuous monitoring, was validated by the intensified fluorescent intensities of CP-preconcentrated analytes and the associated enhanced electrochemical response using differential pulse voltammetry and chronoamperometry. The system performance was evaluated by varying the location of the active electrochemical sensor, target analyte concentrations, and electrolyte concentration using fluorescein molecules as the model analyte and Homovanillic acid (HVA) as the target bioanalyte within both phosphate-buffered saline (PBS) and artificial sweat solution. The combination of on-chip electrochemical sensing with CP-based preconcentration renders this generic approach adaptable to various analytes. This advanced system shows remarkable promise for enhancing biosensing detection in practical applications while bridging the gap between fundamental research and practical implementation.

Label-Free, Non-Optical Readout of Bead-Based Immunoassays with and without Electrokinetic Preconcentration.

In this article, we report a microfluidic bead-based lateral flow immunoassay (LFIA) with a novel sensing mechanism for label-free, non-optical detection of protein binding. This device comprises two packed beds of microbeads: first, bioconjugated microbeads that serve as a test line, and second, a three-dimensional (3D) electrode for sensing. As the protein target binds the bioconjugated microbeads, a shift in ionic conductivity across the bioconjugated beads is produced and can be directly measured at the surface of the 3D electrode by obtaining current-voltage curves before and after incubation of the analyte. We use a model antigen, rabbit IgG, for quantitative evaluation of this sensor, obtaining a limit of detection (LOD) of 50 nM for the LFIA. We demonstrate that this device can be used to measure binding kinetics, exhibiting a rapid (<3 min) increase in the signal after the introduction of the analyte and an exponential decay in the signal after replacing the sample with buffer only. To improve the LOD of our system, we implement an electrokinetic preconcentration technique, faradaic ion concentration polarization (fICP), to increase the local concentration of antigen available during binding as well as the time the antigen interacts with the test line. Our results indicate that this enrichment-enhanced assay (fICP-LFIA) has an LOD of 370 pM, an 135-fold improvement over the LFIA and a 7-fold improvement in sensitivity. We anticipate that this device can be readily adapted for point-of-care diagnostics and translated to any desired protein target by simply modifying the biorecognition agent on these off-the-shelf microbeads.

On-line dual-stage enrichment via magneto-extraction and electrokinetic preconcentration: A new concept and instrumentation for capillary electrophoresis

This study reports on the development of a new concept of on-line dual preconcentration stages for capillary electrophoresis (CE), in which two completely different preconcentration approaches can be realized in the same capillary. In the first stage, a dynamic magneto-extraction of target analytes on circulating magnetic beads is implemented within the capillary. In the second one, electrokinetic preconcentration of eluted analytes via large volume sample stacking is carried out to focus them into a nano band, prior to CE separation of enriched analytes. To implement the dual-stage preconcentration operation, a purpose-made instrument was designed, combining electrophoretic and microfluidic modules to allow precise control of the movement of magnetic beads and analyte's flow. The potential of this new enrichment principle and its associated instrument was demonstrated for CE separation with light-emitting-diode-induced fluorescent (LEDIF) detection of target double-stranded DNA (ds-DNA). The workflow consists of purification and preconcentration of a target DNA fragment (300 bp) on negatively charged magnetic beads, followed by in-capillary elution and fluorescent labelling of the enriched DNA. Large volume sample stacking of the DNA eluent was then triggered to further preconcentrate the labelled DNA before its analysis by CE-LEDIF. An enrichment factor of 125 was achieved for the target DNA fragment. With our new approach, dual-stage sample pretreatment and CE separation can now be performed in-capillary without any mismatch of working volumes, nor any waste of pretreated samples.

Online large volume sample staking preconcentration and separation of enantiomeric GHRH analogs by capillary electrophoresis.

A capillary electrophoresis method is proposed to analyze the four most well-known growth hormone-releasing hormone (GHRH) analogs that are misused by athletes. Dimethyl-β-cyclodextrin used as a chiral selector allowed, for the first time, the separation of those basic peptide analogs, including enantiopeptides (sermorelin and CJC-1293) that differ by the chirality of only one amino acid. To increase the method sensitivity, electrokinetic preconcentration methods have been investigated. The large volume sample stacking with polarity switching (PS-LVSS) method with an injected sample volume corresponding to 80% of the capillary one was found superior to the sweeping in terms of signal enhancement factor (SEF). Acid and organic solvent addition to the sample (0.1mM phosphoric acid with 30% methanol) led to a twofold signal improvement, when compared to water as a matrix. We increased capillary dimensions to provide a signal enhancement through the injection of a larger sample volume. Finally, using a combination of the optimized PS-LVSS preconcentration with the chiral capillary zone electrophoresis (CZE), the GHRH analogs were separated and limits of detection between 75 and 200ng/mL were reached. This method was successfully applied to urine after a desalting step. An optimized C18 SPE was used for that purpose in order to provide low sample conductivity (<130µS/cm) and preserve the efficiency of LVSS preconcentration. SEF of 640 was obtained with desalted urine spiked with sermorelin by comparison to the CZE (without preconcentration) method.

Label-free detection and discrimination of respiratory pathogens based on electrochemical synthesis of biomaterials-mediated plasmonic composites and machine learning analysis

Seasonal outbreaks of respiratory viral infections remain a global concern, with increasing morbidity and mortality rates recorded annually. Timely and false responses contribute to the widespread of respiratory pathogenic diseases owing to similar symptoms at an early stage and subclinical infection. The prevention of emerging novel viruses and variants is also a big challenge. Reliable point-of-care diagnostic assays for early infection diagnosis play a critical role in the response to threats of epidemics or pandemics. We developed a facile method for specifically identifying different viruses based on surface-enhanced Raman spectroscopy (SERS) with pathogen-mediated composite materials on Au nanodimple electrodes and machine learning (ML) analyses. Virus particles were trapped in three-dimensional plasmonic concave spaces of the electrode via electrokinetic preconcentration, and Au films were simultaneously electrodeposited, leading to the acquisition of intense and in-situ SERS signals from the Au–virus composites for ultrasensitive SERS detection. The method was useful for rapid detection analysis (<15 min), and the ML analysis for specific identification of eight virus species, including human influenza A viruses (i.e., H1N1 and H3N2 strains), human rhinovirus, and human coronavirus, was conducted. The highly accurate classification was achieved using the principal component analysis-support vector machine (98.9%) and convolutional neural network (93.5%) models. This ML-associated SERS technique demonstrated high feasibility for direct multiplex detection of different virus species for on-site applications.

An electrokinetic preconcentration trapping pattern in electromembrane microfluidics

Electrokinetic flows near ion-selective membranes, which produce field amplification and electrokinetic preconcentration, have broad applications in preconcentration engineering since almost all electrochemical chips live in saline surroundings. Despite some published work related to electrokinetic molecular concentration, the electrokinetic trapping pattern has not yet been investigated in previous experimental and theoretical studies. By finite element simulations, the paper is concerned with the transition behavior of the trapping pattern in a membrane-embedded microfluidic channel. Regulating the cross-membrane voltage, Debye number, and surface charge, the local interaction of electric field force and electro-osmotic flow distorts the trapping location, resulting in the realization of a series of trapping patterns switches. We find the transition behavior of the trapping pattern in a membrane-embedded microfluidic channel, from a plateau preconcentration plug outside the vortex to a plug with a Gaussian-like distribution and even to a final spike-like pattern of stagnation points inside the vortex. For a small Debye number, the trapping patterns are characterized by stagnation points, an electrokinetic preconcentration pattern formed inside the vortex, and a concentration with spike-like shapes. Upon increasing the cross-membrane voltage and surface charge, the effect of local vortices can modulate the scaling behavior of enrichment factors at the stagnation points, yet the platform preconcentration plug is basically consistent with the existing experimental observations. These intriguing phenomenological patterns have promising applications in separation, desalination, and electrochemistry.

Nucleic Acid Detection with Ion Concentration Polarization Microfluidic Chip for Reduced Cycle Numbers of Polymerase Chain Reaction.

Nucleic acid detection is widely used in disease diagnosis, food safety, environmental monitoring and many other research fields. The continuous development of rapid and sensitive new methods to detective nucleic acid is very important for practical application. In this study, we developed a rapid nucleic-acid detection method using polymerase chain reaction (PCR) combined with electrokinetic preconcentration based on ion concentration polarization (ICP). Using a Nafion film, the proposed ICP microfluidic chip is utilized to enrich the nucleic acid molecules amplified by PCR thermal cycles. To demonstrate the capability of the microfluidic device and the hybrid nucleic-acid detection method, we present an animal-derived component detection experiment for meat product identification applications. With the reduced cycle numbers of 24 cycles, the detection can be completed in about 35 min. The experimental results show that this work can provide a microfluidic device and straightforward method for rapid detection of nucleic acids with reduced cycle numbers.

Electrokinetic Preconcentration and Label-Free Electrical Detection of Sars-Cov-2 RNA at a Packed Bed of Bioconjugated Microspheres

In diagnostics, point-of-care (POC) devices, such as lateral flow assays, play an important role due to their ease of use, practical application, and fast response. However, one of the major limitations of POC devices is low sensitivity. To address this limitation, electrokinetic techniques have been utilized to enrich the target analyte prior to detection. In one such technique, ion concentration polarization (ICP), an ion depleted zone (IDZ) is formed near an ion permselective membrane or electrode following the application of an external electric field. The low conductivity of the IDZ supports the formation of an extended electric field gradient. Enrichment arises from focusing of a charged analyte along this electric field gradient in the presence of opposing fluid flow. ICP focusing is a reliable technique for the enrichment and mobility-based separation of charged species, such as DNA, RNA, or proteins. However, ICP focusing is negatively impacted by electroconvective vortices that drive unwanted mixing.We utilize an out-of-plane faradaic ion concentration polarization (fICP) technique that employs a 3D porous electrode and an adjacent packed bed of insulating microbeads to improve the stability of the enriched plug. In this work, we exhibit the detection of SARS-CoV-2 RNA, extracted from lysed virus, at subpicomolar concentrations in this microfluidic device. Here, the insulating beads are bioconjugated with an uncharged peptide nucleic acid (PNA) oligoprobe that hybridizes with the target RNA. The resulting increase in negative charge on the bead surface leads to a shift in a current-voltage curve between the 3D electrode and a driving electrode at the microchannel inlet. This shift in conductivity serves as a non-optical sensing mechanism for detection of the hybridized SARS-CoV-2 RNA. Most notably, this enrichment and sensing scheme utilizes off-the-shelf streptavidin-modified beads, making it highly versatile, while the reagent-free approach and low driving voltage render it amenable to POC implementation.This work is supported by a grant from the Roy J. Carver Charitable Trust.

Organic Anion Detection with Functionalized SERS Substrates via Coupled Electrokinetic Preconcentration, Analyte Capture, and Charge Transfer.

Detecting ultralow concentrations of anionic analytes in solution by surface-enhanced Raman spectroscopy (SERS) remains challenging due to their low affinity for SERS substrates. Two strategies were examined to enable in situ, liquid phase detection using 5(6)-carboxyfluorescein (5(6)-FAM) as a model analyte: functionalization of a gold nanopillar substrate with cationic cysteamine self-assembled monolayer (CA-SAM) and electrokinetic preconcentration (EP-SERS) with potentials ranging from 0 to +500 mV. The CA-SAM did not enable detection without an applied field, likely due to insufficient accumulation of 5(6)-FAM on the substrate surface limited by passive diffusion. 5(6)-FAM could only be reliably detected with an applied electric field with the charged molecules driven by electroconvection to the substrate surface and the SERS intensity following the Langmuir adsorption model. The obtained limits of detection (LODs) with an applied field were 97.5 and 6.4 nM on bare and CA-SAM substrates, respectively. For the CA-SAM substrates, both the ligand and analyte displayed an ∼15-fold signal enhancement with an applied field, revealing an additional enhancement due to charge-transfer resonance taking place between the metal and 5(6)-FAM that improved the LOD by an order of magnitude.

A compact microfluidic geometry for multiplexing enzyme-linked immunosorbent assays.

We have previously reported a novel approach to implementing multiplex enzyme-linked immunosorbent assay (ELISA) in connected microchannels by exploiting the slow diffusion of the enzyme reaction product across the different assay segments. This work builds on that report by implementing the noted assay in segments arranged along the circumference of a circular channel layout to reduce the footprint size and sample volume requirement. Using the current design, a 5-plex cytokine ELISA was demonstrated in a 1.5×1.5-cm region, which corresponded to a reduction in the footprint area by about a factor of 3 compared to that reported in our previous study. Additionally, the selective coating of our assay segments with the target molecules was realized in this work using electroosmosis instead of hydrodynamic flow as was the case in the previous report. This aspect of our experimental design is particularly significant as it permits the use of cross-sectional channel dimensions significantly shorter than those employed in the current work. Moreover, the use of an electric field for coating purposes enables the integration of functionalities such as electrokinetic preconcentration of analyte molecules during the sample incubation period that can further enhance the capabilities of our assay method.

Tribo-electrophoresis preconcentration enhanced ultra-sensitive SERS detection

Attracting target molecules in solution to electromagnetic hot spots is one of the most important problems in the application of surface-enhanced Raman spectroscopy (SERS). In this work, an ultrasensitive SERS detection system with electrokinetic preconcentration is proposed, in which triboelectric nanogenerator (TENG) is employed to provide the electrostatic driving force for molecular enrichment on SERS substrate. During TENG operation, an electric field is generated in solution and provides sufficient driving force for the movement of target molecules. Thanks to the unique output characteristics of TENG, effective enrichment of molecules in triboelectric preconcentration (TEPC) is achieved in 30 s, which exhibits much higher efficiency compared to the enrichment in 10 min with a DC source. Moreover, the TEPC assisted SERS detection system exhibits excellent sensitivity with the limit of detection (LOD) at 10−15 M. Furthermore, a self-powered TEPC assisted SERS system is designed, which could use environmental mechanical energy and realize outdoor real-time sensitive detection.

High sensitivity capillary electrophoresis with fluorescent detection for glycan mapping

We present in this study a novel strategy to drastically improve the detection sensitivity and peak capacity for capillary electrophoresis with laser induced fluorescent detection (CE-LIF) of glucose oligomers and released glycans. This is based on a new approach exploiting a polymer-free background electrolyte (BGE) for CE-LIF of glycans. The best performance in terms of sample stacking and suppression of electroosmotic flow (EOF) was found for a BGE composed of triethanolamine/citric acid and triethanolamine/acetic acid at elevated ionic strengths (IS up to 200 mM). Compared to the conventional protocols for CE-LIF of glucose-oligosaccharides and released glycans, our polymer-free strategy offered up to 5-fold improvement of detection sensitivity and visualization of higher degree of polymerization (DP) of glucose oligomers (18 vs 15). To further improve the detection sensitivity, a new electrokinetic preconcentration strategy via large volume sample stacking with electroosmotic modulation without having recourse to neutrally coated capillaries is proposed, offering a 200-fold signal enhancement. This approach is based on variation of the buffer's IS, rather than pH adjustment as in conventional methods, for EOF modulation or quasi-total reduction. This strategy allows selecting with high flexibility the best pH conditions to perform efficient preconcentration and separation. The new approach was demonstrated to be applicable for the analysis of N-linked oligosaccharides released from a model glycoprotein (Human Immunoglobulin G) and applied to map N-glycans from human serum for congenital disorders of glycosylation (CDG) diagnosis.

Electroosmotic flow modulation for improved electrokinetic preconcentration: Application to capillary electrophoresis of fluorescent magnetic nanoparticles

It is reported in this study a new approach for modulation and even suppression of the electroosmotic flow (EOF) to achieve better electrokinetic preconcentration in capillary electrophoresis. This is based on the augmentation of the buffer’s concentrations to very high levels (more than a thousand of mM) without recourse to any dynamic/permanent coating nor viscous gel. The use of large weakly charged molecules as background electrolyte’s constituents allows working at extreme concentration ranges without penalty of high electric currents and Joule heating. By this way, the electroosmotic mobility could be modulated over a wide range (2–60 × 10−5 cm2 V−1 s−1 under alkaline conditions), and suppressed to levels equivalent to those obtained with several neutral coatings. The highest buffer concentrations, and the lowest EOF magnitudes, accordingly, were achieved with diethanolamine/3-(Cyclohexylamino)-1-propanesulfonic acid (ionic strength (IS) of 250 mM, pH 9.5), Tris(hydroxymethyl)aminomethane (Tris)/2-(Cyclohexylamino)ethanesulfonic acid (CHES) (IS of 280 mM, pH 8.7) and triethanolamine/2-(Cyclohexylamino)ethanesulfonic acid (IS of 250 mM, pH 8.5). For demonstration, this new approach was applied for sensitive determination of core-shell magnetic nanoparticles (CSMNPs) having high potential for healthcare applications such as imaging agents for diagnostics and controllable cargos for nanomedicine. Different profiles were achieved for purpose-made and commercial magnetic nanoparticles using CE coupled with light-emitting-diode induced fluorescence (LEDIF) detection. The best performance for EOF-assisted preconcentration and CE-LEDIF of CSMNPs was achieved with these nanoparticles prepared in TRIS/CHES (IS 10 mM, pH 8.4) for preconcentration, and separation under BGE of TRIS/CHES (IS 100 mM, pH 8.4). Compared to the conventional capillary electrophoresis (CE-UV) method for characterization of magnetic nanoparticles, our proposed approach with fluorescent detection and EOF-assisted preconcentration offers almost 350-fold sensitivity improvement. Furthermore, our scheme can be used for monitoring the interaction between CSMNPs and target pharmaceutical molecules, serving for drug delivery development. A preliminary study with two antibiotics using this approach revealed that kanamycin interacts better with the target nanoparticles than amikacin.

Microfluidic Electrokinetic Preconcentration Chips: Enhancing the detection of nucleic acids and exosomes

Over the past few years, the detection of biological analytes has intensively been studied to understand the biodiagnostics of various diseases [1]. Some of the analytes that have been used as biomarkers for specific diseases include cell-free nucleic acids, (for example, DNA), messenger RNA (mRNA) and microRNA (miRNA) [2]-[5], circulating tumor-specific nucleic acids [circulating tumor DNA (ctDNA) and ctRNA] [6]-[8], exosomes [9], [10], and circulating tumor cells [11]. These biomolecules are known to be effective indicators that can diagnose the presence of a potential disease even if their concentration changes slightly [12].

Enhancing the sensitivity of point-of-use electrochemical microfluidic sensors by ion concentration polarisation – A case study on arsenic

Point of use (POU) sensors are extremely relevant, being capable of providing fast and reliable analysis in remote and resource-limited settings. Of all the diverse techniques utilised for POU sensors, a combination of electrochemistry and microfluidics may have the greatest potential towards quantitative assessment of heavy metal ions. The major challenge in combining these for sensing applications lies in the complexity of fabricating integrated devices and the insufficient quantity of analytes in the sample volume. To address these issues, we have developed a radial microfluidic device capable of electrokinetic preconcentration by ion concentration polarization (ICP) and integrated it with electroactive surfaces. The proposed sensor is the first demonstration of concentration of heavy metal ions by ICP and its quantitative assessment by voltammetry. Utilising the integrated sensor, we have shown the sensing of As3+ down to 1 ppb by linear sweep voltammetry with ∼40 μL of sample. The sensor was also tested successfully for sensing As3+ in a field sample from an arsenic affected region of India. The sensor was also tested for the detection of other metal ions too. This work would facilitate the development of highly sensitive POU hand-held sensors for water quality monitoring in resource-limited areas.

Speed and sensitivity – Integration of electrokinetic preconcentration with a leaky waveguide biosensor

Improving the limit of detection by preconcentration and reducing the response time of optical biosensors are key requirements to enable their use in point of care (PoC) applications. To address these requirements, we have shown that integration of isoelectric focusing (IEF) at a pH step with a leaky waveguide (LW) sensor containing a non-specific affinity ligand (reactive blue 4 dye (RB4)) can reduce the limit of detection of an exemplar protein (bovine serum albumin (BSA)) by a factor of 600–930 and reduce the response time to < 60 s. This is 6–9 times better preconcentration and up to 16 times faster response time than previous reports. IEF was performed with standard ampholytes and with simple acids and bases forming a pH step. Using ampholytes gave good preconcentration, but was much slower than using a pH step. The LW sensor used a thin agarose hydrogel layer into which RB4 was immobilized. The dye acted both as a non-specific affinity ligand and to visualize the waveguide resonances. This allowed the refractive index of the waveguide to be monitored in real time at any point along the 10 mm separation channel length.

Antibody-free detection of amyloid beta peptides biomarkers in cerebrospinal fluid using capillary isotachophoresis coupled with mass spectrometry

This study reports a capillary isotachophoresis (ITP) – electrospray ionization mass spectrometry (ESI-MS) method for the determination of several amyloid β (Aβ) peptides, which are biomarkers of Alzheimer’s disease (AD) in cerebrospinal fluids (CSF). For the first time, these peptides have been detected directly from CSF by MS without recourse to an immunocapture-based sample pre-treatment. The antibody-free approach is based on the marriage between capillary ITP, a powerful on-line electrokinetic preconcentration technique, and MS for simultaneous detection of different Aβ peptides. To ensure a good performance, the ITP process of fluorescently labelled Aβ peptides was for the first time implemented and verified with laser induced fluorescent detection, prior to methodology transfer to MS detection. Better detection sensitivity was achieved with labelled Aβ peptides for both detection modes. Using hydroxyl ions as the terminating and acetate as the leading ions, our method allows efficient ITP preconcentration under alkaline conditions of the slowly migrating Aβ peptides to reach quantifiable concentration down to 50 pM. The developed ITP-MS approach allows reliable quantification of different fluorescently derivatized Aβ peptides, i.e. Aβ 1–42, Aβ 1–40 and Aβ 1–38 down to sub nM ranges in CSF samples from AD and non-demented (healthy control) patients. Good agreement (<20% deviation) for the determination of Aβ 1–42/Aβ 1–40 ratio in CSF was achieved between results obtained with this new ITP-MS and our recently developed method based on large volume sample stacking coupled to CE. Discrimination of one AD patient from two healthy controls was successfully made with the Aβ 1–42/Aβ 1–40 ratio obtained by the developed ITP-MS method for the tested cerebrospinal fluid samples.

Ultra-sensitive analysis based on electrochemistry, electrokinetic and magnetic preconcentration of analytes

Abstract Some of the challenges with detection of ultra-low concentrations of analytes are to achieve sufficient sensitivity of the measurement and to direct the analyte species to the sensor (electrode) surface. This review describes various strategies that are available to address these challenges: method of electrocatalytic amplification, electrochemical measurements performed in combination with electrokinetic preconcentration of analytes, ultra-sensitive analysis utilizing increased surface area and also the manipulation by the magnetic force.