Pg mL-1 Research Articles

Early diagnosis of autoimmune diseases through electrochemical biosensing using a modified plastic chip electrode.

Detecting chronic autoimmune disorders (ADs) early reduces the risk of morbidity, disability, and mortality and offers the possibility of significant therapeutic action in a timely manner. Developing low-cost, reliable, and sensitive sensors for ADs can ensure the efficient utilization of healthcare resources at earlier stages. Here, we report on the development of an electrochemical biosensor for sensing CXCL10, a chemokine protein that serves as a biomarker for autoimmune diseases. A self-assembly strategy is used for the immobilization of biorecognition elements on a plastic chip electrode (PCE). A homemade PCE offers a versatile and cost-effective scaffold for sensing applications. Gold nanoparticles were electrochemically deposited on the electrode via the reduction of gold ions on the PCE galvanostatically. The CXCL10 antibody and recognition elements were immobilized on the gold-deposited PCE. The attachment of recognition molecules was confirmed by energy-dispersive scanning electron microscopy, atomic force microscopy, infrared spectroscopy, and electrochemical techniques. Electrochemical impedance spectroscopy (EIS) was used for the detection of CXCL10 within a concentration range spanning from pico- to micro-molar levels. The sensor exhibited remarkable linearity in both buffer and plasma solutions, with a limit of detection (LOD) of up to 0.72 pg mL-1.

A reagentless molecularly imprinted polymer-based electrochemical biosensor for single-step detection of troponin I in biofluids.

Reagentless molecular-imprinted polymer (MIP) electrochemical biosensors can offer the next generation of biosensing platforms for the detection of biomarkers owing to their simplicity, cost-efficacy, tunability, robustness, and accuracy. In this work, a novel combination of Prussian blue (PB), coated as an embedded redox probe on a gold working electrode (GWE), and a signal-off MIP assay has been proposed in an electrochemical format for the detection of troponin I (TnI) in biofluids. TnI is a variant exclusive to heart muscles, and its elevated level in the bloodstream is indicative of acute myocardial infarction (AMI). The proposed lab-manufactured PB/MIP electrochemical biosensor, consisting of a simple signal-off MIP assay and a PB redox probe embedded on the GWE surface, is the first of its kind that allows for reagentless, label-free, and single-step electrochemical biosensing of proteins. The preparation steps of the biosensor were fully characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), and Raman spectroscopy. Finally, the performance of the optimized biosensor was investigated through the determination of various concentrations of TnI, ranging from 10 to 100 pg mL-1 within 5 min, in serum and plasma with limits of detection less than 3.6 pg mL-1, and evaluation of selectivity towards TnI using some relevant proteins that exist in biofluids with higher concentrations.

A liposome-based assay for cancer biomarker detection: exploring the correlation between platelet-derived microvesicles and NSCLC-associated miRNAs.

Advances in molecular biology have enabled the identification of numerous cancer biomarkers, offering the potential to improve the diagnosis and prognosis of cancer. In non-small cell lung cancer (NSCLC), the role of platelet-derived microvesicles (PMVs) in cancer progression has received limited attention. While previous studies have focused on the increase of extracellular vesicles in plasma and their interaction with cancer, the expression of microRNAs (miRNAs) delivered through PMVs following platelet activation has remained largely unexplored. This study fills this knowledge gap by investigating miRNA expression in PMVs isolated from healthy donors and NSCLC patients following calcium treatment, a known platelet activator. A significant correlation was found between PMV levels and the expression of specific miRNAs; specifically, miRNA-21 expression increased 7.89 ± 0.44-fold in NSCLC patients and 7.12 ± 0.49-fold in healthy donors after calcium treatment. These findings highlight the potential of PMVs and their miRNA cargo to serve as specific biomarkers for NSCLC, offering valuable insights into cancer diagnosis and prognosis. To facilitate the sensitive detection of these miRNAs, a novel carboxyfluorescein (CF)-loaded liposome-based assay was developed. This assay demonstrated enhanced sensitivity, achieving a detection limit of 1.03 pg mL-1, when combined with a calcium platelet-activation approach. This research has the potential to lead to the development of innovative diagnostic tools and therapeutic strategies, ultimately improving outcomes for patients with NSCLC and other cancers.

A prototype of ultrasensitive time-resolved fluoroimmunoassay for the quantitation of lead in plasma using a fluorescence-enhanced europium chelate label for the detection system.

This study describes the prototype of a novel ultra-sensitive time-resolved fluoroimmunoassay (TRFIA) for the quantification of lead (Pb) in plasma. The assay procedures were conducted in 96-microwell plates and involved the competitive binding format. The assay used a mouse monoclonal antibody, designated as 2C33, that specifically recognized the diethylenetriamine pentaacetic acid chelate of Pb (Pb-DTPA) but did not recognize Pb-free DTPA chelator. The antigen used for coating onto the inner surfaces of assay plate microwells was Pb-DTPA conjugated with bovine serum albumin protein (Pb-DTPA-BSA). The competitive binding reaction occurred between Pb-DTPA chelates, formed in the sample solutions by treating the samples with an excess DTPA, and the coated Pb-DTPA-BSA for a limited quantity of 2C33 antibody binding sites. The antigen-antibody complex formed in the plate wells was quantified by a europium-DTPA-labeled secondary antibody and a fluorescence enhancement solution. The conditions of the assay were refined, and its optimum procedures were established. The TRFIA was validated following the immunoassay validation guidelines, and all of the validation criteria were acceptable. The working range of the assay was 20-300 pg mL-1 and its limit of quantitation was 20 pg mL-1. Metals that are commonly encountered in blood plasma did not interfere with Pb in the analysis by the proposed TRFIA. The assay was applied to the quantitation of Pb in plasma samples with satisfactory accuracy and precision. The results were compared favorably with those obtained by atomic emission spectroscopy. In conclusion, the present study represents the first TRFIA for the quantitation of Pb in plasma. The assay is superior to the existing atomic spectrometric methods and other immunoassays for Pb in terms of sensitivity, convenience, and analysis throughputs. The proposed TRFIA is anticipated to effectively contribute to assessing Pb concentrations and controlling the exposure of humans to its potential toxicity.

Detecting carcinoembryonic antigen based on the aggregation-induced emission enhancement effect.

In this study, a novel label-free fluorescent aptasensor with an aggregation-induced emission enhancement effect was developed and applied for the detection of carcinoembryonic antigen (CEA). The sensor has a simple detection mechanism, easy operation, high sensitivity (with low limit of detection of 1 pg mL-1), good selectivity, and wide linear range (0.003-10 ng mL-1). In addition, it can be directly applied for the determination of CEA in human serum.

Cu-MOFs@AuPtNPs nanozyme-based immunosorbent assay for colorimetric detection of alpha-fetoprotein.

Accurate detection of tumor biomarkers in blood is crucial for diagnosing and treating tumor disease. In this study, a metal enzyme-linked immunosorbent assay (MeLISA) was fabricated for the ultrasensitive and naked-eye detection of tumor biomarker alpha-fetoprotein (AFP) in clinical serum samples. Herein, novel copper metal-organic frameworks and gold platinum nanoparticle composites (Cu-MOFs@AuPtNPs) were synthesized for the first time by an in situ method, which showed an enormous specific surface area and excellent peroxidase (POx) mimicking properties. Cu-MOFs@AuPtNPs linked with antibodies targeting AFP served as a signal nanoprobe to amplify the detection signal. Additionally, the specificity of MeLISA was significantly enhanced through a conventional antigen-antibody reaction and efficient blocking of non-specific sites with BSA. Under optimal conditions, the sandwich-type MeLISA exhibited a wide range from 0.001 to 1000 ng mL-1 (R2 = 0.997) and a low detection limit of 0.86 pg mL-1 (S/N = 3) with acceptable stability, selectivity, and reproducibility. It is noteworthy that the suggested MeLISA performed exceptionally well in detecting clinical serum samples, which were visible to the naked eye and did not require complex platforms. To sum up, the innovative MeLISA based on Cu-MOFs@AuPtNPs provides an alternative method for early cancer diagnosis, particularly in economically backward areas where simple diagnostic apparatus is extremely desirable.

A sandwich-type photoelectrochemical biosensor based on Ru(bpy)32+ sensitized In2S3 for aflatoxin B1 detection.

Aflatoxin B1 (AFB1), classified as a class I carcinogen, is a widespread mycotoxin that poses a serious threat to public health and economic development, and the food safety problems caused by AFB1 have aroused worldwide concern. The development of accurate and sensitive methods for the detection of AFB1 is significant for food safety monitoring. In this work, a sandwich-type photoelectrochemical (PEC) biosensor for AFB1 detection was constructed on the basis of an aptamer-antibody structure. A good photocurrent response was obtained due to the sensitization of In2S3 by Ru(bpy)32+. In addition, this sandwich-type sensor constructed by modification with the antibody, target detector, and aptamer layer by layer attenuated the migration hindering effect of photogenerated carriers caused by the double antibody structure. The aptamer and antibody synergistically recognized and captured the target analyte, resulting in more reliable PEC response signals. CdSe@CdS QDs-Apt were modified as a signal-off probe onto the sensor platform to quantitatively detect AFB1 with a "signal-off" response, which enhanced the sensitivity of the sensor. The PEC biosensor showed a linear response range from 10-12 to 10-6 g mL-1 with a detection limit of 0.023 pg mL-1, providing a feasible approach for the quantitative detection of AFB1 in food samples.

Simultaneous binding of carboxyl and amino groups to liquid metal surface for biosensing.

Eutectic gallium indium (EGaIn) nanoparticles can be modified with aniline derivatives to introduce versatile functional groups toward bioapplications beyond materials science. p-Aminobenzoic acid (PABA) modified EGaIn (EGaIn-PABA) demonstrated high wettability due to the presence of carboxyl groups, but the priority of binding of carboxyl and amino groups on the EGaIn surface remains unclear. To study the binding nature of PABA to EGaIn, the anti-mouse IgG antibody labeled with fluorescein isothiocyanate (FITC) (IgG-FITC) was covalently modified to EGaIn-PABA to verify the presence of terminal carboxyl groups on the EGaIn surface. The binding of gold nanoparticles (AuNPs) to EGaIn-PABA nanoparticles suggested the presence of terminal amino groups on the EGaIn surface. Then, taking advantage of the reductive nature of amino groups, the Almar blue fluorescence experiment was designed to determine the co-existence of carboxyl and amino groups on the EGaIn-PABA surface with an approximate ratio of 3 : 7, suggesting that carboxyl groups had a higher probability of binding with the EGaIn surface than that of amino groups. Then, an aptasensor was fabricated on the EGaIn-PABA surface with AuNPs for electrochemical detection of interleukin-6 with a sensitivity of 1 pg mL-1.

Antenna effect enhanced ECL immunoassay using microfloral europium porphyrin coordination polymers based on Eu3+ and TCPP for the detection of chloramphenicol in foods.

The "antenna effect" is one of the most important energy transfer modes in lanthanide light-emitting polymers. In this study, novel luminescent nanostructured coordination polymers (Eu-PCP) were synthesized in one step using Eu3+ as the central metal ion and 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) as the organic ligand. The unique "antenna effect" observed between Eu3+ and TCPP leads to a substantial improvement in the electrochemiluminescence (ECL) emission efficiency. Eu-PCP exhibits good cathodic ECL characteristics. Additionally, Au@SnS2 nanosheets exhibit favorable electrical conductivity, biocompatibility, and a significant specific surface area. This makes them a suitable choice as substrate materials for the modification of electrode surfaces and capturing antigens. Being well known, the development of sensitive and rapid methods to detect chloramphenicol is essential for food safety. Based on this, we report a novel competitive electrochemiluminescence immunoassay to achieve ultra-sensitive and highly specific detection of chloramphenicol. The linear range was 0.0002-500 ng mL-1 and the detection limit was 0.09 pg mL-1. Apart from that, the experimental results proved that it provided a new analytical tool for the detection of antibiotic residues in food safety.

Single-molecule microfluidic assay for prostate-specific antigen based on magnetic beads and upconversion nanoparticles.

Early-stage diagnosis of prostatic carcinoma is essential for successful treatment and, thus, significant prognosis improvement. In laboratory practice, the standard non-invasive diagnostic approach is the immunochemical detection of the associated biomarker, prostate-specific antigen (PSA). Ultrasensitive detection of PSA is essential for both diagnostic and recurrence monitoring purposes. To achieve exceptional sensitivity, we have developed a microfluidic device with a flow-through cell for single-molecule analysis using photon-upconversion nanoparticles (UCNPs) as a detection label. For this purpose, magnetic microparticles (MBs) were first optimized for the capture and preconcentration of PSA and then used to implement a bead-based upconversion-linked immunoassay (ULISA) in the microfluidic device. The digital readout based on counting single nanoparticle-labeled PSA molecules on MBs enabled a detection limit of 1.04 pg mL-1 (36 fM) in 50% fetal bovine serum, which is an 11-fold improvement over the respective analog MB-based ULISA. The microfluidic technique conferred several other advantages, such as easy implementation and the potential for achieving high-throughput analysis. Finally, it was proven that the microfluidic setup is suitable for clinical sample analysis, showing a good correlation with a reference electrochemiluminescence assay (recovery rates between 97% and 105%).

Detection of carbofuran in fruits and vegetables by Raman spectroscopy combined with immunochromatography.

It has long been desired to develop rapid methods for the rapid identification and quantification of pesticides and their metabolites. Carbofuran, a representative pesticide of the carbamate group, is highly systemic and is used on vegetables, fruits and grains, which has led many countries to test for residues in food and the environment. In this study, gold and silver composite core-shell (Au@Ag) nanoparticles were used to label the carbofuran antibody and Raman molecule 5,5-dithiobis-2-nitrobenzoic acid (DTNB) to synthesize Raman immune probes. The signal value of DTNB was read using a Raman spectrometer, and the quantitative detection technology of carbofuran was established based on lateral flow immunochromatographic assay (ICA) combined with surface-enhanced Raman spectroscopy (SERS). SERS-ICA is a rapid, quantitative and ultrasensitive test for the determination of carbofuran in fruits and vegetables with a sensitivity of 0.1 pg mL-1. Consequently, the results demonstrate that the SERS-based lateral flow immunosensor developed in this study has the advantages of excellent assay sensitivity and remarkable multiplexing capability, and thus it will have great application potential in food safety monitoring.

AuNPs-BP-MWCNTs-COOH-based electrochemical immunosensor for the determination of deoxynivalenol in wheat flour.

Deoxynivalenol (DON) has drawn considerable attention for its obvious pathogenicity and wide use in agro-products, which cause a potential threat to human health. In this work, an electrochemical immunosensor is developed for the highly sensitive and selective detection of DON in wheat flour using AuNPs-BP-MWCNTs-COOH and antibodies. The AuNPs-BP-MWCNTs-COOH nanocomposite was prepared via an in situ reduction reaction and ultrasonic-assisted liquid-phase exfoliation. The nanocomposite exhibits a larger surface area, decent stability, excellent electron transfer capability, good protein binding capability and prominent specificity. The plentiful carboxyl group on the nanocomposite can bind to the amino group of the antibody, and AuNPs have an affinity for the sulfhydryl group of the antibody, which makes it feasible for the nanocomposite to load the antibody. The peak currents are plotted against the logarithm of DON concentration from 0.002 to 80 ng mL-1 with a limit of detection (LOD) of 0.5 pg mL-1. This approach establishes an effective label-free immunosensor platform for the detection of DON with high sensitivity and selectivity in various food and agricultural products.

Automatic microdispenser-integrated multiplex enzyme-linked immunosorbent assay device with autonomously driven centrifugal microfluidic system.

In this study, we established the control and design theory of an autonomously driven dispenser at a steady rotation speed and proposed a dispenser-integrated multiplex enzyme-linked immunosorbent assay (ELISA) device. In establishing the theory of the dispenser, we estimated the flow rate in the dispenser and the applied pressure onto the passive valves, so that the suitable burst pressure of the valves and flow rate could be designed. The dispenser-integrated multiplex ELISA device has the potential to perform flow control for executing an ELISA of 6 samples/standards per chip or 18 samples/standards per compact disk by just steadily rotating a chip. In the immunoassay evaluation of the device using mouse IgG detection, it was confirmed that the device could assay 5 μL of several standards in just 30 min without nonspecific reactions, and although this system has a high limit of detection (LOD, 63.4-164 pg mL-1) it is equal to that of manual assay with a titer plate. The device can be fabricated by transferring the microchannel pattern from a mold without complex assembly or alignment, and it can control the liquid operation by just steadily rotating. Thus, the device system developed will contribute to reducing the cost of fabricating chips and control equipment for ELISA systems. Consequently, a compact, portable, and low-cost ELISA system for point-of-care testing is expected to be realized.

A broad-spectrum peptide screening method using an optimized solid-phase extraction and liquid chromatography-high-field asymmetric ion mobility spectrometry-mass spectrometry for doping control in equine urine.

The abuse of prohibited peptide-based drugs with a broad spectrum of chemical characteristics poses a significant concern for the horseracing industry. Recently, there has been a notable increase in positive cases of small-peptide drugs reported in equine and canine sports. In addition to small peptides, large peptides (over 2 kDa) with structural diversity have also entered the market in increasing numbers as drugs for humans and livestock. However, the simultaneous analysis of both small- and large-peptide-based drugs is still challenging. In this study, a screening method was developed to cover 74 analytes, including peptides, their catabolites, and/or their mimetics, with molecular weights ranging from 0.3 kDa to greater than 5 kDa. The simultaneous extraction of both small and large peptides was achieved using a weak cation-exchange solid-phase extraction cartridge with a mixture of different pore sizes (suitable for large peptides), followed by analysis using liquid chromatography high-field asymmetric ion mobility spectrometry tandem mass spectrometry (LC-FAIMS-MS/MS). For method validation, the limits of detection (LoDs), reproducibility, recovery, matrix effect, selectivity, and carryover were evaluated. Remarkably, the LoDs of ∼80% of the analytes were less than or equal to 50 pg ml-1, with the lowest LoD (1 pg ml-1) being observed for selected peptides in horse urine. These results indicate a substantial advancement in achieving comprehensive coverage for both small and large peptides with high sensitivity for the purpose of doping control in horseracing and equestrian sports.

Facile, green and scalable synthesis of single-layer manganese dioxide nanosheets and its application for GSH and cTnI colorimetric detection.

Manganese dioxide (MnO2) nanosheets possess unique physical and chemical properties, making them widely applicable in various fields, such as chemistry and biomedicine. Although MnO2 nanosheets are produced using bottom-up wet chemistry synthesis methods, their scale is below the gram level and requires a long processing time, restricting their effective scale-up from laboratory to market. We report a facile, green and scalable synthesis of MnO2 nanosheets by mixing Shiranui mandarin orange juice and KMnO4 for 30 minutes. We produced more than one gram (1.095) of MnO2 nanosheets with a 0.65 nm mean thickness and a 50 nm mean lateral size. Furthermore, we established a visual colorimetric biosensing strategy based on MnO2 nanosheets for the assay of glutathione (GSH) and cardiac troponin I (cTnI), offering high sensitivity and feasibility in clinical samples. For GSH, the limit of detection was 0.08 nM, and for cTnI, it was 0.70 pg mL-1. Meanwhile, the strategy can be used for real-time analysis by applying a smartphone-enabled biosensing strategy, which can provide point-of-care testing in remote areas.

Split-type photoelectrochemical immunoassay for sensitive quantification of carcinoembryonic antigen based on target-induced in situ formation of Z-type heterojunction.

Carcinoembryonic antigen (CEA), a vital biomarker, plays a significant role in the early diagnosis and prognostic estimation of malignant tumors. In this study, a split-type photoelectrochemical immunoassay for the sensitive quantification of CEA has been successfully developed based on the target-induced in situ formation of a Z-type heterojunction. First, gold nanoparticle-decorated ZnIn2S4 (AuNPs/ZnIn2S4) composites were synthesized and used for the fabrication of photoelectrodes. Then, the detection antibody labeled with Ag nanoparticles was formed and applied for the biorecognition of CEA and subsequent liberation of Ag+ ions to induce the in situ formation of Ag2S/AuNPs/ZnIn2S4, a Z-type heterojunction, on the photoelectrode. The Z-type Ag2S/AuNPs/ZnIn2S4 heterojunction with effectively promoted separation of photogenerated charge carriers could lead to a markedly enhanced photocurrent response and highly sensitive quantification of CEA. Moreover, the three-dimensional spatial structure of ZnIn2S4 provides abundant active sites for the reaction and exhibits non-enzymatic properties, which are conducive to the further improvement of the analytical performance of CEA. The developed split-type photoelectrochemical immunoassay with good sensitivity, satisfactory selectivity, reliable stability, wide dynamic linear range (0.01-20 ng mL-1), and low detection limit (7.3 pg mL-1) offers valuable insights into the development of novel PEC biosensing models for the detection of tumor biomarkers and holds potential application value in the field of disease diagnosis.

Oxygen-bridged W-Pd atomic pairs enable H2O2 activation for sensitive immunoassays.

Regulating the performance of peroxidase (POD)-like nanozymes is a prerequisite for achieving highly sensitive and accurate immunoassays. Inspired by natural enzyme catalysis, we design a highly active and selective nanozyme by loading atomically dispersed tungsten (W) sites on Pd metallene (W-O-Pdene) to construct an artificial three-dimensional (3D) catalytic center. The 3D asymmetric W-O-Pd atomic pairs can effectively stretch the O-O bonds in H2O2 and further promote the desorption of H2O to enhance POD-like activity. Moreover, the W-O-Pd sites with unique spatial structures demonstrate satisfactory specificity for H2O2 activation, effectively preventing the interference of dissolved oxygen. Accordingly, the highly active and specific W-O-Pdene nanozymes are utilized for sensitive and accurate prostate-specific antigen (PSA) immunoassay with a low detection limit of 1.92 pg mL-1, superior to commercial enzyme-linked immunosorbent assay.

Establishment and characterization of noro-VLP measurement by digital ELISA.

Highly sensitive viral analytical techniques are essential tools for preventing the spread of infections. In this study, we established a digital enzyme-linked immunosorbent assay (ELISA) system to quantify norovirus proteins with high sensitivity. We used norovirus-like particles (noro-VLPs) as a surrogate for norovirus and constructed two digital ELISA systems using two different antibody pairs. The quantitative performance of the noro-VLP measurement using each digital ELISA system was evaluated. Both assay systems exhibited high sensitivity, good linearity, and high stability. The first system exhibited a limit of detection (LOD) of 87 pg mL-1 and correlation coefficient (R2) of 0.9984. Analysis of samples containing 5 ng per mL noro-VLP confirmed inter-assay variation of 5.5%, and intra-assay variation of 5.2%. The second system exhibited an LOD of 19 pg mL-1 and R2 of 0.9984. Analysis of samples containing 5 ng per mL noro-VLP confirmed inter-assay variation of 4.5%, and intra-assay variation of 2.5%. Comparison of the two systems using the same calibrant for unpurified and fractionated noro-VLPs revealed that the quantitative values for unpurified noro-VLPs were the same, whereas those for fractionated noro-VLPs were dramatically different. Our findings indicate that the reactivity to various components in the noro-VLP solution was altered depending on the different antibodies. Furthermore, our study highlights the importance of using appropriate calibrants, which contain the same ratio of components as the noro-VLP analyte, to afford accurate measurements.

Microfluidic finger-actuated mixer for ultrasensitive electrochemical measurements of protein biomarkers for point-of-care testing.

Current diagnostic tests for high sensitivity detection of protein biomarkers involve long incubation times or require bulky/expensive instrumentation, hindering their use for point-of-care testing. Here, we report a microfluidic electrochemical immunosensor that employs a unique finger-actuated mixer for rapid, ultrasensitive measurements of protein biomarkers. Mixing was implemented during the incubation steps, which accelerated biomolecular transport and promoted immunocomplex formation, leading to enhanced analytical sensitivity and a shortened detection time. Electrochemical measurements were performed using a handheld diagnostic device consisting of a smartphone and miniature potentiostat. Proof of principle was demonstrated by using this platform for quantitative measurements of C-X-C motif chemokine ligand 9 (CXCL9), a serological biomarker for autoimmune and inflammatory diseases, which could be detected in human plasma at concentrations as low as 4.7 pg mL-1 in <25 min. The ability to rapidly detect protein biomarkers with high sensitivity in a point-of-care format makes this device a promising tool for diagnostic testing, particularly in resource-limited settings.

Electrochemical immunomagnetic assay for interleukin-6 detection in human plasma.

An electrochemical immunoassay for interleukin-6 (IL-6) was developed based on IL-6 capture using magnetic beads and electrochemical signal production using horseradish peroxidase/tetramethylbenzidine. We achieved IL-6 detection from the 50-1000 pg mL-1 range, which is a physiologically relevant IL-6 range for a variety of biological systems. The sandwich assay performed well in phosphate buffered solution as well as in cellular media and human plasma spiked with IL-6, and decreased time to IL-6 concentration readout to approximately one hour. There is also future potential to apply this assay to real-time point-of-care human disease diagnostics.