Isotachophoresis with Oscillating Sample Zones to Control the Spatial Overlap of Co-focused Species

Microfluidic isotachophoresis (ITP) is a powerful technique that can significantly increase the reaction rate of homogeneous chemical reactions by cofocusing reactants in a narrow sample zone. Correspondingly, ITP has been utilized to reduce the reaction time in various bioanalytical assays. However, in conventional ITP, it is hardly possible to control the reaction rate in real time, i.e., speeding up or slowing down a reaction on demand. Here, we experimentally demonstrate a new mode of ITP that allows the spatial overlap of two ITP zones to be precisely controlled over time, which is a crucial first step toward controlling reaction rates. Two nonreactive samples are initially focused and separated by a spacer using a DC electric field. By superimposing an oscillating field component with sufficiently high amplitude on the DC field, the spatial overlap of their concentration profiles is temporarily increased due to electromigration dispersion. The time-average of this overlap can be precisely controlled by varying the frequency and amplitude of the oscillation. We suggest that this scheme can be transferred to chemical reactions between ionic species with sufficiently different electrophoretic mobilities. Tuning the parameters of the oscillatory electric field should allow direct control of the corresponding reaction rate.

Isotachophoresis: Theory and Microfluidic Applications

Isotachophoresis (ITP) is a versatile electrophoretic technique that can be used for sample preconcentration, separation, purification, and mixing, and to control and accelerate chemical reactions. Although the basic technique is nearly a century old and widely used, there is a persistent need for an easily approachable, succinct, and rigorous review of ITP theory and analysis. This is important because the interest and adoption of the technique has grown over the last two decades, especially with its implementation in microfluidics and integration with on-chip chemical and biochemical assays. We here provide a review of ITP theory starting from physicochemical first-principles, including conservation of species, conservation of current, approximation of charge neutrality, pH equilibrium of weak electrolytes, and so-called regulating functions that govern transport dynamics, with a strong emphasis on steady and unsteady transport. We combine these generally applicable (to all types of ITP) theoretical discussions with applications of ITP in the field of microfluidic systems, particularly on-chip biochemical analyses. Our discussion includes principles that govern the ITP focusing of weak and strong electrolytes; ITP dynamics in peak and plateau modes; a review of simulation tools, experimental tools, and detection methods; applications of ITP for on-chip separations and trace analyte manipulation; and design considerations and challenges for microfluidic ITP systems. We conclude with remarks on possible future research directions. The intent of this review is to help make ITP analysis and design principles more accessible to the scientific and engineering communities and to provide a rigorous basis for the increased adoption of ITP in microfluidics.

Isotachophoresis for rapid transformation of Escherichia coli

A frequent limitation of electroporation (EP) and chemical transformation (CT) are the need of tedious and time-consuming procedures for inducing transformation competence, the substantial number of cells required, and the low transformation yields typically achieved. Here, we show a new and rapid electrokinetic method for transformation of small number of noncompetent Escherichia coli TOP10 cells (2-3 × 10⁵ ) at room temperature. Escherichia coli TOP10 cells and plasmid DNA are sequentially injected into a 50 μm ID capillary and focused into 11.5 nL by isotachophoresis (ITP) induced by application of high DC voltage (-16 kV). Through ITP, a large excess of plasmid DNA is brought in contact with the cell surface, with the contact time adjusted by application of a counter-pressure (1.3 psi) opposing the ITP movement. The transformation rate was more than 1000-fold higher compared to EP and CT at survival rates greater than 60%.

Lectins applied to diagnosis and treatment of prostate cancer and benign hyperplasia: A review

Environmental factors, as well as genetic factors, contribute to the increase in prostate cancer cases (PCa), the second leading cause of cancer death in men. This fact calls for the development of more reliable, quick and low-cost early detection tests to distinguish between malignant and benign cases. Abnormal cell glycosylation pattern is a promising PCa marker for this purpose. Proteins, such as lectins can decode the information contained in the glycosylation patterns. Several studies have reported on applications of plant lectins as diagnostic tools for PCa considering the ability to differentiate it from benign cases. In addition, they can be used to detect, separate and differentiate the glycosylation patterns of cells or proteins present in serum, urine and semen. Herein, we present an overview of these studies, showing the lectins that map glycans differentially expressed in PCa, as well as benign hyperplasia (BPH). We further review their applications in biosensors, histochemical tests, immunoassays, chromatography, arrays and, finally, their therapeutic potential. This is the first study to review vegetable lectins applied specifically to PCa.

Highly sensitive Lens culinaris agglutinin-reactive fraction of α-fetoprotein is a predictive marker for hepatocarcinogenesis in long-term observation of patients with chronic liver disease

Highly sensitive Lens culinaris agglutinin-reactive fraction of α-fetoprotein (hs-AFP-L3) is a specific marker for hepatocellular carcinoma (HCC) and has been reliable in cases with a low serum α-fetoprotein (AFP) level. However, the biomarkers that contribute to hepatocarcinogenesis during the long-term observation are not yet clear. The present study reported the clinical utility of hs-AFP-L3 in the long-term observation of patients with chronic liver disease. The subjects were 106 patients with chronic liver disease without HCC or a history of HCC treatment and who had been followed for >12 months. hs-AFP-L3 was measured using cryopreserved serum. The factors contributing to hepatocarcinogenesis were examined using univariate and multivariate analyses. The median observation period was 88 months (15-132 months). The cumulative incidence of HCC was 10.5% at 5 years and 19.6% at 10 years. The univariate analysis revealed that age ≥55 years old, platelet count ≤13.1x10⁴/µl, hyaluronic acid ≥80.8 ng/ml, alanine transaminase ≥47 U/l, AFP ≥6.3 ng/ml, hs-AFP-L3 ≥3.5% and des-γ-carboxy prothrombin (DCP) ≥25 mAU/ml were significant factors. In the multivariate analysis, platelet count ≤13.1x10⁴/µl [hazard ratio (HR), 4.966; 95% confidence interval (CI), 1.597-15.437; P=0.006] and hs-AFP-L3 ≥3.5% (HR, 5.450; 95% CI, 1.522-19.512; P=0.009) were extracted as significant factors contributing to hepatocarcinogenesis. In addition, for cases with AFP <20 ng/ml, a multivariate analysis revealed that hs-AFP-L3 ≥4.9% (HR, 11.608; 95% CI, 2.422-55.629; P=0.002) and DCP ≥25 mAU/ml (HR, 3.936; 95% CI, 1.088-14.231; P=0.037) were significant factors contributing to hepatocarcinogenesis. hs-AFP-L3 is a useful marker for predicting hepatocarcinogenesis in the long-term observation of patients with chronic liver disease.

Serum core-type fucosylated prostate-specific antigen index for the detection of high-risk prostate cancer

It is known that core-type fucosylation is higher in prostate cancer cells than in other cancer cell types and is associated with high-risk prostate cancer. Here, we developed an automated microcapillary electrophoresis-based immunoassay system for measuring serum core-type fucosylated prostate-specific antigen (PSA) and evaluated whether the serum fucosylated PSA index (FPI) can detect high-risk prostate cancer. Core-type fucosylated-free PSA was measured by our automated microcapillary electrophoresis-based immunoassay system with Pholiota squarrosa lectin. The FPI was calculated from total PSA and the percentage of fucosylated-free PSA. The optimum model to predict Gleason grade (GG) ≥2 was constructed by multivariate logistic regression analysis. Discrimination was assessed by determining the area under the receiver operator characteristic curve (AUC). The study included 252 men who underwent prostate needle biopsy due to elevated serum PSA levels (4-20 ng/mL), including 138 with GG ≥2. A higher FPI was significantly associated with GG (P < .0001). Multivariate logistic regression analysis showed that age, prostate volume and FPI were significant predictors of GG ≥2. The AUC of FPI and the model were 0.729 (95% confidence interval [CI]: 0.668-0.790) and 0.837 (95% CI: 0.788-0.886), respectively, compared to 0.629 (95% CI: 0.561-0.698) for PSA. Decision curve analysis showed the superior benefit of FPI and the model when compared to PSA. In a cohort with serum PSA levels <20 ng/mL, FPI could differentiate high-risk prostate cancer from biopsy-negative or low-risk prostate cancer. Therefore, FPI could be a useful adjunct in prostate biopsy counseling for men with abnormal PSA levels.

Capillary electrophoresis-based immunoassay and aptamer assay: A review

Over the last two decades, the group of techniques called affinity probe CE has been widely used for the detection and the determination of several types of biomolecules with high sensitivity. These techniques combine the low sample consumption and high separation power of CE with the selectivity of the probe to the target molecule. The assays can be defined according to the type of probe used: CE immunoassays, with an antibody as the probe, or aptamer-based CE, with an aptamer as the probe. Immunoassays are generally divided into homogeneous and heterogeneous groups, and homogeneous variant can be further performed in competitive or noncompetitive formats. Interacting partners are free in solution at homogeneous assay, as opposed to heterogeneous analyses, where one of them is immobilized onto a solid support. Highly sensitive fluorescence, chemiluminescence or electrochemical detections were typically used in this type of study. The use of the aptamers as probes has several advantages over antibodies such as shorter generation time, higher thermal stability, lower price, and lower variability. The aptamer-based CE technique was in practice utilized for the determination of proteins in biological fluids and environmentally or clinically important small molecules. Both techniques were also transferred to microchip. This review is focused on theoretical principles of these techniques and a summary of their applications in research.

A decade of microchip electrophoresis for clinical diagnostics - A review of 2008-2017

A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient samples. To obtain relevant and reliable information, a methodological approach of sample preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological samples are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.

Isotachophoresis applied to biomolecular reactions

This review discusses research developments and applications of isotachophoresis (ITP) to the initiation, control, and acceleration of chemical reactions, emphasizing reactions involving biomolecular reactants such as nucleic acids, proteins, and live cells. ITP is a versatile technique which requires no specific geometric design or material, and is compatible with a wide range of microfluidic and automated platforms. Though ITP has traditionally been used as a purification and separation technique, recent years have seen its emergence as a method to automate and speed up chemical reactions. ITP has been used to demonstrate up to 14 000-fold acceleration of nucleic acid assays, and has been used to enhance lateral flow and other immunoassays, and even whole bacterial cell detection assays. We here classify these studies into two categories: homogeneous (all reactants in solution) and heterogeneous (at least one reactant immobilized on a solid surface) assay configurations. For each category, we review and describe physical modeling and scaling of ITP-aided reaction assays, and elucidate key principles in ITP assay design. We summarize experimental advances, and identify common threads and approaches which researchers have used to optimize assay performance. Lastly, we propose unaddressed challenges and opportunities that could further improve these applications of ITP.

An Automated Micro-Total Immunoassay System for Measuring Cancer-Associated α2,3-linked Sialyl N-Glycan-Carrying Prostate-Specific Antigen May Improve the Accuracy of Prostate Cancer Diagnosis

The low specificity of the prostate-specific antigen (PSA) for early detection of prostate cancer (PCa) is a major issue worldwide. The aim of this study to examine whether the serum PCa-associated α2,3-linked sialyl N-glycan-carrying PSA (S2,3PSA) ratio measured by automated micro-total immunoassay systems (μTAS system) can be applied as a diagnostic marker of PCa. The μTAS system can utilize affinity-based separation involving noncovalent interaction between the immunocomplex of S2,3PSA and Maackia amurensis lectin to simultaneously determine concentrations of free PSA and S2,3PSA. To validate quantitative performance, both recombinant S2,3PSA and benign-associated α2,6-linked sialyl N-glycan-carrying PSA (S2,6PSA) purified from culture supernatant of PSA cDNA transiently-transfected Chinese hamster ovary (CHO)-K1 cells were used as standard protein. Between 2007 and 2016, fifty patients with biopsy-proven PCa were pair-matched for age and PSA levels, with the same number of benign prostatic hyperplasia (BPH) patients used to validate the diagnostic performance of serum S2,3PSA ratio. A recombinant S2,3PSA- and S2,6PSA-spiked sample was clearly discriminated by μTAS system. Limit of detection of S2,3PSA was 0.05 ng/mL and coefficient variation was less than 3.1%. The area under the curve (AUC) for detection of PCa for the S2,3PSA ratio (%S2,3PSA) with cutoff value 43.85% (AUC; 0.8340) was much superior to total PSA (AUC; 0.5062) using validation sample set. Although the present results are preliminary, the newly developed μTAS platform for measuring %S2,3PSA can achieve the required assay performance specifications for use in the practical and clinical setting and may improve the accuracy of PCa diagnosis. Additional validation studies are warranted.

Lab on a stick: multi-analyte cellular assays in a microfluidic dipstick

A new microfluidic concept for multi-analyte testing in a dipstick format is presented, termed "Lab-on-a-Stick", that combines the simplicity of dipstick tests with the high performance of microfluidic devices. Lab-on-a-stick tests are ideally suited to analysis of particulate samples such as mammalian or bacterial cells, and capable of performing multiple different parallel microfluidic assays when dipped into a single sample with results recorded optically. The utility of this new diagnostics format was demonstrated by performing three types of multiplex cellular assays that are challenging to perform in conventional dipsticks: 1) instantaneous ABO blood typing; 2) microbial identification; and 3) antibiotic minimum inhibitory (MIC) concentration measurement. A pressure balance model closely predicted the superficial flow velocities in individual capillaries, that were overestimated by up to one order of magnitude by the Lucas-Washburn equation conventionally used for wicking in cylindrical pores. Lab-on-a-stick provides a cost-effective, simple, portable and flexible multiplex platform for a range of assays, and will deliver a new generation of advanced yet affordable point-of-care tests for global diagnostics.

Application of cancer-associated glycoforms and glycan-binding probes to an in vitro diagnostic multivariate index assay for precise diagnoses of cancer

Personalized medicine has emerged as a widely accepted trend in medicine for the efficacious and safe treatment of various diseases. It covers every medical treatment tailored according to various properties of individuals. Cancer-associated glycosylation mirrors cancer states more precisely, and this "sweet side of cancer" is thus intended to spur the development of an advanced in vitro diagnostic system. The changes of glyco-codes are often subtle and thus not easy to trace, thereby making it difficult to discriminate changes from various compounding factors. Special glycan-binding probes, often lectins, can be paired with aglycosylated antibodies to enable quantitative and qualitative measurements of glycoforms. With the in vitro diagnosis multivariate index assay (IVDMIA) considered to be capable of yielding patient-specific results, the combinatorial use of multiple glycoproteins may be a good modality to ensure disease-specific, personalized diagnoses.

Biomarkers for Hepatocellular Carcinoma (HCC): An Update

The past decades have witnessed increased use of biomarkers in disease management. A biomarker is any characteristic that can be objectively measured and evaluated as an indicator of normal biological process, pathogenic process, or pharmacological response to a therapeutic intervention. The clinical measurements of biomarkers can be carried out in vivo using imaging modalities like ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI), as well as in vitro utilizing serum or plasma or other body fluids as specimens. In contrast to the imaging modalities, a prominent value of serum biomarkers is that they could be biologically relevant and disease-specific to pathophysiologic or pathologic process of disease development. This article provides an update of serum biomarkers for hepatocellular carcinoma (HCC) in risk assessment for early detection through surveillance.

Rapid Slow Off-Rate Modified Aptamer (SOMAmer)-Based Detection of C-Reactive Protein Using Isotachophoresis and an Ionic Spacer

We present an on-chip electrophoretic assay for rapid protein detection with a SOMAmer (Slow Off-Rate Modified Aptamer) reagent. We used isotachophoresis (ITP) coupled with an ionic spacer to both react and separate SOMAmer-protein complex from free SOMAmer reagent. ITP accelerates the reaction kinetics as the ionic spacer concurrently separates the reaction products. We developed a numerical and analytical model to describe ITP spacer assays, which involve low-mobility, nonfocusing targets that are recruited into the ITP zone by higher-mobility, ITP-focused probes. We demonstrated a proof-of-concept of this assay using C-reactive protein (CRP) in buffer, and achieved a 2 nM limit of detection (LOD) with a combined 20 min assay time (10 min off-chip preparation of reagents and 10 min on-chip run). Our findings suggest that this approach has potential as a simple and rapid alternative to other homogeneous immunoassays. We also explore the extension of this assay to a diluted serum sample spiked with CRP, where we observe decreased sensitivity (an LOD of 25 nM in 20-fold diluted serum). We describe the challenges in extending this assay to complex samples and achieving higher sensitivity and specificity for clinical applications.

Increase of fucosylated alpha-fetoprotein fraction at the onset of autoimmune hepatitis and acute liver failure

AIM

Increased serum α-fetoprotein (AFP) has been associated with a good prognosis following acute liver failure (ALF), but the levels of the fucosylated fraction of AFP (Lens culinaris agglutinin-reactive fraction of AFP [AFP-L3]) following acute liver injury remain unknown. The aim of the present study was to investigate the clinical significance of AFP and AFP-L3 in patients with acute liver injury.

METHODS

We investigated the serum levels of AFP and highly sensitive AFP-L3% in 27 patients with acute-onset autoimmune hepatitis (AIH), 28 patients with acute hepatitis (AH) and 22 patients with ALF at the onset using a highly sensitive immunoassay (micro-total analysis system).

RESULTS

The serum AFP levels were increased in patients with AIH, AH and ALF, but the levels did not significantly differ among them. However, the mean AFP-L3% level was significantly higher in patients with AIH than in patients with AH (P = 0.0039). Moreover, significantly more patients with AIH demonstrated AFP-L3 positivity (≥10%) when compared with patients with AH (P = 0.014). Although the percentage of AFP-L3 positivity increased with AFP levels, at low serum AFP levels (<10 ng/mL), significantly more patients with AIH demonstrated AFP-L3 positivity than did patients with AH (P = 0.024) or ALF (P = 0.038).

CONCLUSION

We demonstrated for the first time that highly sensitive AFP-L3% levels were increased at the onset of AIH. The mechanism underlying the increase in AFP-L3 remains to be elucidated, but this finding may reflect an alteration of the glycosylation such as hyperfucosylation, which can influence the modifications of self-antigens in hepatocytes.

Cationic isotachophoresis separation of the biomarker cardiac troponin I from a high-abundance contaminant, serum albumin

Cationic ITP was used to separate and concentrate fluorescently tagged cardiac troponin I (cTnI) from two proteins with similar isoelectric properties in a PMMA straight-channel microfluidic chip. In an initial set of experiments, cTnI was effectively separated from R-Phycoerythrin using cationic ITP in a pH 8 buffer system. Then, a second set of experiments was conducted in which cTnI was separated from a serum contaminant, albumin. Each experiment took ∼10 min or less at low electric field strengths (34 V/cm) and demonstrated that cationic ITP could be used as an on-chip removal technique to isolate cTnI from albumin. In addition to the experimental work, a 1D numerical simulation of our cationic ITP experiments has been included to qualitatively validate experimental observations.

Microfluidic electrophoretic mobility shift assays for quantitative biochemical analysis

Electrophoretic mobility shift assays (EMSAs) play an important role in analytical chemistry, quantitative bioscience, and point-of-care diagnostics. Emerging microfluidic lab-on-a-chip technologies bring high throughput and multiplexed analysis to affinity-based electrophoretic separations, greatly advancing the performance of traditional EMSAs. This review elaborates on the relevant theoretical basis for EMSAs, surveys microfluidic-based EMSA applications in molecular conformation analyses, immunoassays, affinity assays and genomics, and outlines challenges and potential future improvements needed from this powerful assay.

Clinical applications of capillary electrophoresis based immunoassays

Immunoassays have long been an important set of tools in clinical laboratories for the detection, diagnosis, and treatment of disease. Over the last two decades, there has been growing interest in utilizing CE as a means for conducting immunoassays with clinical samples. The resulting method is known as a CE immunoassay. This approach makes use of the selective and strong binding of antibodies for their targets, as is employed in a traditional immunoassay, and combines this with the speed, efficiency, and small sample requirements of CE. This review discusses the variety of ways in which CE immunoassays have been employed with clinical samples. An overview of the formats and detection modes that have been employed in these applications is first presented. A more detailed discussion is then given on the type of clinical targets and samples that have been measured or studied by using CE immunoassays. Particular attention is given to the use of this method in the fields of endocrinology, pharmaceutical measurements, protein and peptide analysis, immunology, infectious disease detection, and oncology. Representative applications in each of these areas are described, with these examples involving work with both traditional and microanalytical CE systems.

Prognostic role of pre-treatment serum AFP-L3% in hepatocellular carcinoma: systematic review and meta-analysis

Background

Serum lens culinaris agglutinin-reactive fraction of α-fetoprotein (AFP-L3%) has been widely used for HCC diagnosis and follow-up surveillance as tumor serologic marker. However, the prognostic value of high pre-treatment serum AFP-L3% in patients with hepatocellular carcinoma (HCC) remains controversial. We therefore conduct a meta-analysis to assess the relationship between high pre-treatment serum AFP-L3% and clinical outcome of HCC.

Methods

Eligible studies were identified through systematic literature searches. A meta-analysis of fifteen studies (4,465 patients) was carried out to evaluate the association between high pre-treatment serum AFP-L3% and overall survival (OS) and disease-free survival (DFS) in HCC patients. Sensitivity and subgroup analyses were also conducted in this meta-analysis.

Results

Our analysis results showed that high pre-treatment serum AFP-L3% implied poor OS (HR: 1.65, 95%CI: 1.45–1.89 p<0.00001) and DFS (HR: 1.80, 95% CI: 1.49–2.17 p<0.00001) of HCC. Subgroup analysis revealed that there was association between pre-treatment serum AFP-L3% and endpoint (OS and DFS) in low AFP concentration HCC patients (HR: 1.96, 95% CI: 1.24–3.10, p = 0.004; HR: 2.53, 95% CI: 1.09–5.89, p = 0.03, respectively).

Conclusion

The current evidence suggests that high pre-treatment serum AFP-L3% levels indicated a poor prognosis for patients with HCC and AFP-L3% may have significant prognostic value in HCC patients with low AFP concentration.

Alpha-fetoprotein-L3 in hepatocellular carcinoma: a meta-analysis

BACKGROUND AND OBJECTIVE

Alpha-fetoprotein (AFP) has been widely used as a diagnostic marker. AFP is also increased in patients at high risk for hepatocellular carcinoma (HCC), ie those with chronic hepatitis. The percentage of lens culinaris agglutinin-reactive alpha-fetoprotein (AFP-L3%) has long been proposed as a marker for HCC, but has not been widely adopted due to inconsistent results reported in the literature. In this study, the performance of AFP-L3% is specifically evaluated for diagnosis of HCC.

METHODS

A systematic review of relevant studies, the sensitivity, specificity, and diagnostic odds ratio (DOR) for the diagnosis of HCC were pooled using random-effects models. The overall test performance was summarized using summary receiver operating characteristic (SROC) curve analysis. Potential between-study heterogeneity was explored by meta-regression model.

RESULTS

Twelve articles were included in this meta-analysis. The overall estimates of AFP-L3% in detecting HCC were as follows: pooled sensitivity, 0.483 (95% confidence interval (CI) 0.459-0.507); pooled specificity, 0.929 (95% CI 0.916-0.940); DOR, 12.33 (95% CI 7.82-19.44); and area under the curve (AUC), 0.7564.

CONCLUSIONS

AFP-L3% could be complementary to AFP as a marker for HCC.

Value of highly sensitive fucosylated fraction of alpha-fetoprotein for prediction of hepatocellular carcinoma recurrence after curative treatment

BACKGROUND

The fucosylated fraction of alpha-fetoprotein (AFP-L3) has been used as a diagnostic marker for hepatocellular carcinoma (HCC). Recently, a highly sensitive immunoassay using an on-chip electrokinetic reaction and separation by affinity electrophoresis (micro-total analysis system; μTAS) has been developed.

AIM

The aim of this study was to investigate the relationship between changes in the serum AFP-L3 level measured by μTAS assay and recurrence of HCC after curative treatment.

METHODS

A total of 414 HCC patients who met the Milan criteria and underwent hepatectomy or radiofrequency ablation were investigated prospectively for the relationship between HCC recurrence and values of tumor markers.

RESULTS

There were significant differences in recurrence-free survival between groups with and without AFP-L3 elevation measured before and after treatment (p = 0.024 and p = 0.001 for before and after treatment, respectively). Multivariate analysis revealed that AFP-L3 status (p = 0.002) measured 1 month after treatment was a significant independent predictor of HCC recurrence after curative treatment.

CONCLUSIONS

Elevation of the serum AFP-L3 level before treatment is a predictor of HCC recurrence, and sustained elevation of the AFP-L3 level after treatment is an indicator of HCC recurrence. Repeated measurement of μTAS AFP-L3 should be performed for surveillance of HCC recurrence after curative treatment.

Rapid hybridization of nucleic acids using isotachophoresis

We use isotachophoresis (ITP) to control and increase the rate of nucleic acid hybridization reactions in free solution. We present a new physical model, validation experiments, and demonstrations of this assay. We studied the coupled physicochemical processes of preconcentration, mixing, and chemical reaction kinetics under ITP. Our experimentally validated model enables a closed form solution for ITP-aided reaction kinetics, and reveals a new characteristic time scale which correctly predicts order 10,000-fold speed-up of chemical reaction rate for order 100 pM reactants, and greater enhancement at lower concentrations. At 500 pM concentration, we measured a reaction time which is 14,000-fold lower than that predicted for standard second-order hybridization. The model and method are generally applicable to acceleration of reactions involving nucleic acids, and may be applicable to a wide range of reactions involving ionic reactants.

Development of an antibody-lectin enzyme immunoassay for fucosylated α-fetoprotein

BACKGROUND

Fucosylation is one of the most important types of glycosylations related to cancer. Our previous studies of the enzymatic basis and structural studies of α-fetoprotein (AFP) samples from liver cancer patients indicated that core-fucosylation by α1,6-fucosyltransferase (FUT8) resulted in the production of fucosylated AFP, and in fact fucosylated AFP allowed differential diagnosis in some types of liver cancer from liver cirrhosis. This served as a predictive biomarker for the development of liver cancer 3 to 18 months before it could be detected using imaging techniques. Fucosylated AFP is currently measured by means of a liquid-phase binding assay (LBA) or by an electrokinetic analyte transport assay (EATA). However, these methods require special instrumentation that is currently available only in major medical laboratories. To overcome this problem, we attempted to develop an enzyme immunoassay (EIA) based on the sandwich technique with specific antibody and lectin.

RESULTS

Dilute solutions of highly fucosylated AFP in human sera were assayed using a microtiter plate coated with a periodate-oxidized anti-AFP antibody, a fucose-specific biotinylated Aleuria aurantia lectin (AAL), a peroxidase-conjugated streptoavidin, and a chemiluminescent detection system. The technique was able to measure highly fucosylated AFP diluted to 5 to 80ng/ml in human sera using the developed antibody-lectin EIA in combination with the enrichment of AFP.

CONCLUSION

A simple method using an antibody-lectin EIA for quantifying fucosylated AFP that does not require special instrumentation was developed.

GENERAL SIGNIFICANCE

The method can be generally applied to the quantitative measurement of various fucosylated glycoproteins using specific antibodies. This article is part of a Special Issue entitled Glycoproteomics.

Preconcentration and detection of the phosphorylated forms of cardiac troponin I in a cascade microchip by cationic isotachophoresis

This paper describes the detection of a cardiac biomarker, cardiac troponin I (cTnI), spiked into depleted human serum using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic channel. The microfluidic chip incorporates a 100× cross-sectional area reduction, including a 10× depth reduction and a 10× width reduction, to increase sensitivity during ITP. The cross-sectional area reductions in combination with ITP allowed visualization of lower concentrations of fluorescently labeled cTnI. ITP was performed in both "peak mode" and "plateau mode" and the final concentrations obtained were linear with initial cTnI concentration. We were able to detect and quantify cTnI at initial concentrations as low as 46 ng mL(-1) in the presence of human serum proteins and obtain cTnI concentrations factors as high as ~ 9000. In addition, preliminary ITP experiments including both labeled cTnI and labeled protein kinase A (PKA) phosphorylated cTnI were performed to visualize ITP migration of different phosphorylated forms of cTnI. The different phosphorylated states of cTnI formed distinct ITP zones between the leading and terminating electrolytes. To our knowledge, this is the first attempt at using ITP in a cascade microchip to quantify cTnI in human serum and detect different phosphorylated forms.

Human tear protein analysis enabled by an alkaline microfluidic homogeneous immunoassay

The ability to probe the protein content of human tear fluid has enormous potential for deepening our understanding of ocular and systemic disease pathology and enabling novel noninvasive tear-based diagnostic technologies. To overcome current challenges in tear proteomic measurements, we report on the first microfluidic homogeneous immunoassay capable of making rapid, quantitative, and specific measurements of endogenous tear protein biomarkers in human tear fluid. Lactoferrin (Lf) is a tear-specific biomarker for Sjögren's syndrome (SS), a serious systemic autoimmune disease currently diagnosed through rudimentary volumetric and surface chemistry measurements and an invasive lip biopsy. We detail optimization of a homogeneous electrophoretic immunoassay for Lf in <1 μL of tear fluid at clinically relevant concentrations. In particular, we present assay development details and a final assay that enables quantification of Lf in <5 s in a clinically relevant range for SS diagnostics. Characterization suggests the on-chip assay is accurate to within 15% of ELISA, specific (<15% nonspecific signal), and with a lower limit of detection of 3 ± 2 nM Lf in human tear matrix. Additionally, we develop and characterize a protocol for eluting proteins from nitrocellulose Schirmer strips, the clinical de facto standard for tear collection and storage. We relate on-chip measured Lf concentrations back to ocular surface concentrations for the first time to our knowledge. Taken in sum, this work details important steps toward (1) expanding the set of proteins quantified by electrophoretic immunoassays to encompass a wider range of isoelectric points than has been reported, (2) creating a first-in-kind translatable assay with clinical relevance to SS diagnostics, and (3) expanding the analytical toolkit available for rapid tear protein measurements, as is relevant to the advancement of basic research and clinical medicine.

Novel Lens culinaris agglutinin-reactive fraction of α-fetoprotein: a biomarker of hepatocellular carcinoma recurrence in patients with low α-fetoprotein concentrations

BACKGROUND

Lens culinaris agglutinin-reactive fraction of α-fetoprotein (AFP-L3) is a specific marker used to detect hepatocellular carcinoma (HCC). However, its clinical utility is not sufficient in patients with low total AFP concentrations because of limitations in instrument sensitivity. Recent advances have led to the introduction of a highly sensitive AFP-L3% assay (sensitive AFP-L3%), provided by a novel on-chip, liquid-phase binding assay. This cross-sectional study was conducted to evaluate the clinical significance of the sensitive AFP-L3% in determining HCC recurrence in patients with low total AFP concentrations.

METHODS

A total of 370 consecutive patients with HCC were screened within 1-3 months of locoregional treatment, and 215 of the 370 patients showed serum AFP <20 ng/ml. Total AFP, sensitive AFP-L3%, and des-gamma-carboxy prothrombin (DCP) were measured in those 215 patients and HCC recurrence was evaluated by radiological findings. Optimal cutoff values of the markers for detecting HCC recurrence were obtained on the basis of receiver operating characteristic (ROC) curve.

RESULTS

The area under the ROC curve of the total AFP, sensitive AFP-L3%, and DCP in HCC patients with serum AFP <20 ng/ml were 0.638, 0.724, and 0.779, respectively. The diagnostic accuracies of the total AFP, sensitive AFP-L3%, and DCP were 60.9% (cutoff value 5 ng/ml), 67.7% (cutoff value 7%), and 64.6% (cutoff value 40 ng/ml), respectively.

CONCLUSIONS

The new sensitive AFP-L3% assay provides great utility in determining HCC recurrence in patients with low AFP concentrations. Further studies focusing on the combinatorial use of the markers (total AFP, sensitive AFP-L3%, and DCP) are required.

A multiplexed immunoassay system based upon reciprocating centrifugal microfluidics

A novel, centrifugal disk-based micro-total analysis system (μTAS) for low cost and high throughput semi-automated immunoassay processing was developed. A key innovation in the disposable immunoassay disk design is in a fluidic structure that enables very efficient micro-mixing based on a reciprocating mechanism in which centrifugal acceleration acting upon a liquid element first generates and stores pneumatic energy that is then released by a reduction of the centrifugal acceleration, resulting in a reversal of direction of flow of the liquid. Through an alternating sequence of high and low centrifugal acceleration, the system reciprocates the flow of liquid within the disk to maximize incubation/hybridization efficiency between antibodies and antigen macromolecules during the incubation/hybridization stage of the assay. The described reciprocating mechanism results in a reduction in processing time and reagent consumption by one order of magnitude.

Microfluidic mixing: a review

The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers.

Clinical significance of the highly sensitive fucosylated fraction of α-fetoprotein in patients with chronic liver disease

BACKGROUND AND AIM

The purpose of the present study was to investigate the clinical significance of the highly sensitive fucosylated fraction of α-fetoprotein (hs-AFP-L3) in patients with chronic liver disease (CLD) and low serum α-fetoprotein (AFP) concentration.

METHODS

A total of 241 patients being treated at our institute with CLD and low serum AFP concentration (3-10 ng/mL) were investigated retrospectively. We measured total AFP and the percentage of AFP-L3 using a µTAS Wako i30 device. The possible presence of hepatocellular carcinoma (HCC) was thoroughly investigated by various examinations carried out from 1 month before to 1 month after measurements. In addition, hs-AFP-L3 elevated and non-elevated groups, divided by the cut-off value based on a receiver-operator characteristic (ROC) curve, were followed for possible future development of HCC.

RESULTS

hs-AFP-L3 was above the detectable range in 60 patients (24.9%). Among those AFP-L3 positive cases, 20 (33.3%) were found to be HCC prevalent, whereas HCC was found in just 16 patients (8.8%) with undetectable hs-AFP-L3 levels. We determined the cut-off value of hs-AFP-L3%, which shows the proportion of AFP L3 in total AFP, to be 5.75%. During the follow-up period, HCC was newly detected in six patients (22.2%) in the hs-AFP-L3% elevated group and in 10 (5.6%) in the non-elevated group. Analysis using the Kaplan-Meier method showed the HCC-free rate of the hs-AFP-L3% elevated group was significantly lower than that of the non-elevated group (P=0.0038). Independent predicting variants were female sex (P=0.0024) and hs-AFP-L3% elevation (P=0.0036).

CONCLUSION

Our results suggest hs-AFP-L3 level is a useful tumor marker for HCC in patients with CLD and low serum AFP concentration.

Immunoaffinity chromatography: an introduction to applications and recent developments

Immunoaffinity chromatography (IAC) combines the use of LC with the specific binding of antibodies or related agents. The resulting method can be used in assays for a particular target or for purification and concentration of analytes prior to further examination by another technique. This review discusses the history and principles of IAC and the various formats that can be used with this method. An overview is given of the general properties of antibodies and of antibody-production methods. The supports and immobilization methods used with antibodies in IAC and the selection of application and elution conditions for IAC are also discussed. Several applications of IAC are considered, including its use in purification, immunodepletion, direct sample analysis, chromatographic immunoassays and combined analysis methods. Recent developments include the use of IAC with CE or MS, ultrafast immunoextraction methods and the use of immunoaffinity columns in microanalytical systems.

10,000-fold concentration increase of the biomarker cardiac troponin I in a reducing union microfluidic chip using cationic isotachophoresis

This paper describes the preconcentration of the biomarker cardiac troponin I (cTnI) and a fluorescent protein (R-phycoerythrin) using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic chip. The microfluidic chip includes a channel with a 5× reduction in depth and a 10× reduction in width. Thus, the overall cross-sectional area decreases by 50× from inlet (anode) to outlet (cathode). The concentration is inversely proportional to the cross-sectional area so that as proteins migrate through the reductions, the concentrations increase proportionally. In addition, the proteins gain additional concentration by ITP. We observe that by performing ITP in a cross-sectional area reducing microfluidic chip we can attain concentration factors greater than 10,000. The starting concentration of cTnI was 2.3 μg mL⁻¹ and the final concentration after ITP concentration in the microfluidic chip was 25.52 ± 1.25 mg mL⁻¹. To the author's knowledge this is the first attempt at concentrating the cardiac biomarker cTnI by ITP. This experimental approach could be coupled to an immunoassay based technique and has the potential to lower limits of detection, increase sensitivity, and quantify different isolated cTnI phosphorylation states.

10,000-fold concentration increase in proteins in a cascade microchip using anionic ITP by a 3-D numerical simulation with experimental results

This paper describes both the experimental application and 3-D numerical simulation of isotachophoresis (ITP) in a 3.2 cm long "cascade" poly(methyl methacrylate) (PMMA) microfluidic chip. The microchip includes 10 × reductions in both the width and depth of the microchannel, which decreases the overall cross-sectional area by a factor of 100 between the inlet (cathode) and outlet (anode). A 3-D numerical simulation of ITP is outlined and is a first example of an ITP simulation in three dimensions. The 3-D numerical simulation uses COMSOL Multiphysics v4.0a to concentrate two generic proteins and monitor protein migration through the microchannel. In performing an ITP simulation on this microchip platform, we observe an increase in concentration by over a factor of more than 10,000 due to the combination of ITP stacking and the reduction in cross-sectional area. Two fluorescent proteins, green fluorescent protein and R-phycoerythrin, were used to experimentally visualize ITP through the fabricated microfluidic chip. The initial concentration of each protein in the sample was 1.995 μg/mL and, after preconcentration by ITP, the final concentrations of the two fluorescent proteins were 32.57 ± 3.63 and 22.81 ± 4.61 mg/mL, respectively. Thus, experimentally the two fluorescent proteins were concentrated by over a factor of 10,000 and show good qualitative agreement with our simulation results.

Clinical advantage of highly sensitive on-chip immunoassay for fucosylated fraction of alpha-fetoprotein in patients with hepatocellular carcinoma

BACKGROUND

Alpha-fetoprotein (AFP) has been widely used as a diagnostic master for hepatocellular carcinoma (HCC), and the fucosylated fraction of AFP (AFP-L3) has been reported to be a specific marker for HCC. However, AFP-L3 has not always been reliable in cases with low serum AFP concentrations. Recently, a novel automated immunoassay for AFP-L3, the micro-total analysis system (μ-TAS), has been developed.

AIM

The aim of this study is to evaluate the clinical usefulness of μ-TAS AFP-L3.

METHODS

Serum AFP-L3 was measured in 295 patients with HCC and in 350 with benign liver diseases. The diagnostic accuracy of μ-TAS AFP-L3 was compared with that of the conventional assay (liquid-phase binding assay; LiBASys). The relationship between μ-TAS AFP-L3 and clinical features was investigated.

RESULTS

When the cutoff value was set at 7%, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of μ-TAS AFP-L3 were 60.0%, 90.3%, 76.4%, 83.9%, and 72.8%, respectively. Its sensitivity was particularly good (41.1%) in HCC subgroups with lower AFP concentrations (<20 ng/ml). The positivity rates for μ-TAS AFP-L3 were higher at each tumor stage than those of LiBASys AFP-L3 (μ-TAS/LiBASys: stage I, 44.2%/16.3%; stage II, 52.9%/37.5%; stage III, 66.4%/44.5%; stage IV, 82.8%/65.5%).

CONCLUSIONS

μ-TAS AFP-L3 is more sensitive for discriminating HCC than the conventional LiBASys AFP-L3, particularly in subgroups with lower AFP concentrations and early-stage HCC.

Ultrashort separation length homogeneous electrophoretic immunoassays using on-chip discontinuous polyacrylamide gels

To realize efficient homogeneous electrophoretic immunoassays, we introduce discontinuous polyacrylamide gels that enable quantitative assay completion in separation lengths as short as 350 mum in <10 s. The discontinuous cross-linked gels reduce the required electrophoretic separation lengths and thereby significantly reduce the required applied electrical potentials needed to achieve 100's V/cm electric field strengths for rapid electrophoresis. To optimize the discontinuous polyacrylamide gel assay format, we demonstrate development of a two-color homogeneous electrophoretic immunoassay for concurrent quantitation of C reactive protein (CRP) and tumor necrosis factor-alpha (TNF-alpha) for monitoring inflammatory response. To achieve necessary pore-size control at the gel discontinuity, an optimized mask-based fabrication protocol is introduced. The fabrication approach improves electrophoretic separations using the discontinuous separation gels by eliminating two confounding phenomena: (1) smaller than desired pores at the discontinuity which result in undesired physical exclusion of large-species and (2) an associated transition from small to large pores aft of the interface which acts to "destack" analyte bands during the separation. With the use of the optimized discontinuous separation gels, both assays were linear and quantitative over a two-log detection range, with a lower limit of detection of 11 ng/mL for CRP and 40 ng/mL for TNF-alpha. An optimal single-point detector location was identified by balancing the separation resolution and assay duration constraints. The ultrashort separation distance electrophoretic assays developed here provide flexibility in chip and instrument design by relaxing electrical potential requirements and expanding the possibilities for assay multiplexing, therefore addressing important design considerations when developing field-portable diagnostic assays for near-patient environments.

Immunoassays in microfluidic systems

Immunoassays have greatly benefited from miniaturization in microfluidic systems. This review, which summarizes developments in microfluidics-based immunoassays since 2000, includes four sections, focusing on the configurations of immunoassays that have been implemented in microfluidics, the main fluid handling modalities that have been used for microfluidic immunoassays, multiplexed immunoassays in microfluidic platforms, and the emergence of label-free detection techniques. The field of microfluidic immunoassays is continuously improving and has great promise for the future.

Integrated microfluidic device for serum biomarker quantitation using either standard addition or a calibration curve

Detection and accurate quantitation of biomarkers such as alpha-fetoprotein (AFP) can be a key aspect of early stage cancer diagnosis. Microfluidic devices provide attractive analysis capabilities, including low sample and reagent consumption, as well as short assay times. However, to date microfluidic analyzers have relied almost exclusively on calibration curves for sample quantitation, which can be problematic for complex mixtures such as human serum. We have fabricated integrated polymer microfluidic systems that can quantitatively determine fluorescently labeled AFP in human serum using either the method of standard addition or a calibration curve. Our microdevices couple an immunoaffinity purification step with rapid microchip electrophoresis separation in a laser-induced fluorescence detection system, all under automated voltage control in a miniaturized polymer microchip. In conjunction with laser-induced fluorescence detection, these systems can quantify AFP at approximately 1 ng/mL levels in approximately 10 microL of human serum in a few tens of minutes. Our polymer microdevices have been applied in determining AFP in spiked serum samples. These integrated microsystems offer excellent potential for rapid, simple, and accurate biomarker quantitation in a point-of-care setting.

Automated immunoassay system for AFP-L3% using on-chip electrokinetic reaction and separation by affinity electrophoresis

Implementation of the on-chip immunoassay for alpha-fetoprotein (AFP)-L3% was achieved using a fully automated microfluidic instrument platform that will prepare the chip and run the assay with a total assay time of less than 10min. Reagent/sample mixing, concentration, and reaction in microfluidic channels occur by the electrokinetic analyte transport assay (EATA) technique, enabling the integration of all assay steps on-chip. The determination of AFP-L3%, a biomarker for hepatocellular carcinoma, was achieved by the presence of Lens culinaris agglutinin in the separation channel, causing separation of the fucosylated isoform, AFP-L3, from the nonfucosylated AFP-L1 by lectin affinity electrophoresis. Laser-induced-fluorescence (LIF) detection was used to quantitate the labeled immunocomplexes. The limit of detection (LOD) was 0.1ng/ml AFP, and assay precision of less than 2% coefficient of variation (CV) was obtained for quantitation from 24 to 922ng/ml total AFP in spiked serum samples. Assay precision of less than 3% CV was obtained for AFP-L3% measurements from 8.5 to 81%. Furthermore, good correlation of test results for 68 patient serum samples with a commercially available reference method (LiBASys assay for AFP-L3%) was obtained, with r(2)=0.981 and slope=1.03.