Detection Of Human Chorionic Gonadotropin Research Articles

Target-mediated silver deposition-based electrochemical biosensor for highly sensitive detection of human chorionic gonadotropin

As a glycoprotein hormone, human chorionic gonadotropin (hCG) is an established marker for pregnancy test. On the basis of the target-mediated silver deposition (TSD), in this work, we report the development of an amplification-free electrochemical biosensor for the highly sensitive detection of hCG. The detection of hCG involves the use of the affinity peptide-modified electrode for hCG capture (the CGGSSPPLRINRHILTR peptide containing the hCG-binding domain of the PPLRINRHILTR sequence is used as the affinity peptide), the oxidation of the diol sites of the glycan chains on hCG hormones into aldehyde groups by NaIO4, and the deposition of silver nanoparticles (AgNPs) for the solid-state voltammetric stripping analysis. Due to the deposition of multiple AgNPs while the solid-state Ag/AgCl voltammetric process has a high signal-to-noise ratio, the TSD-based electrochemical biosensor can be applied to the highly sensitive detection of hCG without the need for signal amplification. Under optimal conditions, the stripping current increased linearly with an increasing hCG concentration over the range from 1.0 to 25 mIU/mL, with a detection limit of 0.45 mIU/mL. Owing to the high specificity of the hCG-binding peptide PPLRINRHILTR, this electrochemical hCG biosensor exhibits high selectivity. The results of the quantitative assay of hCG in urine samples at the concentrations of 25, 10, and 1.0 mIU/mL are desirable, indicating the good anti-interference capability. As the TSD-based electrochemical biosensor allows the amplification-free detection of low-abundance hCG, it is easy to use and cost-effective, showing great promise in point-of-care assay of hCG for pregnancy test.

Construction and evaluation of AuNPs enhanced electrochemical immunosensors with [Fe(CN)6]3−/4− and PPy probe for highly sensitive detection of human chorionic gonadotropin

Human chorionic gonadotropin (HCG), a vital protein for pregnancy determination and a marker for trophoblastic diseases, finds application in monitoring early pregnancy and ectopic pregnancy. This study presents an innovative approach employing electrochemical immunosensors for enhanced HCG detection, utilizing Anti-HCG antibodies and gold nanoparticles (AuNPs) in the sensor platform. Two sensor configurations were optimized: BSA/Anti-HCG/c-AuNPs/MEL/e-AuNPs/SPCE with [Fe(CN)6]3−/4− as a redox probe (1) and BSA/Anti-HCG/PPy/e-AuNPs/SPCE using polypyrrole (PPy) as a redox probe (2). The first sensor offers linear correlation in the 0.10–500.00 pg∙mL−1 HCG range, with a limit of detection (LOD) of 0.06 pg∙mL−1, sensitivity of 32.25 μA∙pg−1∙mL∙cm−2, RSD <2.47 %, and a recovery rate of 101.03–104.81 %. The second sensor widens the HCG detection range (40.00 fg∙mL−1-5.00 pg∙mL−1) with a LOD of 16.53 fg∙mL−1, ensuring precision (RSD <1.04 %) and a recovery range of 94.61–106.07 % in serum samples. These electrochemical immunosensors have transformative potential in biomarker detection, offering enhanced sensitivity, selectivity, and stability for advanced healthcare diagnostics.

Popcorn-like bimetallic palladium/platinum exhibiting enhanced peroxidase-like activity for signal enhancement in lateral flow immunoassay

BackgroundThe lateral flow immunoassay (LFIA) is widely employed as a point-of-care testing (POCT) technique. However, its limited sensitivity hinders its application in detecting biomarkers with low abundance. Recently, the utilization of nanozymes has been implemented to enhance the sensitivity of LFIA by catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The catalytic performance of nanozymes plays a crucial role in influencing the sensitivity of LFIA. ResultsThe Cornus officinalis Sieb. et Zucc-Pd@Pt (CO–Pd@Pt) nanozyme with good peroxidase-like activity was synthesized herein through a facile one-pot method employing Cornus officinalis Sieb. et Zucc extract as a reducing agent. The morphology and composition of the CO–Pd@Pt nanozyme were characterized using TEM, SEM, XRD, and XPS. As a proof of concept, the as-synthesized CO–Pd@Pt nanozyme was utilized in LFIA (CO–Pd@Pt-LFIA) for the detection of human chorionic gonadotropin (hCG). Compared to conventional gold nanoparticles-based LFIA (AuNPs-LFIA), CO–Pd@Pt-LFIA demonstrated a significant enhancement in the limit of detection (LOD, 0.08 mIU/mL), which is approximately 160 times lower than that of AuNPs-LFIA. Furthermore, experiments evaluating accuracy, precision, selectivity, interference, and stability have confirmed the practical applicability of CO–Pd@Pt-LFIA for hCG content determination. SignificanceThe present study presents a novel approach for the synthesis of bimetallic nanozymes through environmentally friendly methods, utilizing plant extracts as both protective and reducing agents. Additionally, an easily implementable technique is proposed to enhance signal detection in lateral flow immunoassays.

A fluorescent immunochromatographic strip based on CsPbBr3/CsPb2Br5@SiO2 facile encapsulation in pure water for the detection of human chorionic gonadotropin (HCG) antigen

Fluorescent immunochromatographic test (FICT) strips have received extensive attention due to their virtue of simple operation, low cost, and a point-of-care (POC) assay. In recent years, people are constantly seeking new labels to improve the sensitivity of immunosensors. Perovskite nanocrystals (PNCs) possess strong fluorescence and a narrow emission peak, making them an excellent choice as a new fluorescent signal label. Herein, we have developed a simple, fast, and environmentally friendly method to synthesize CsPbBr3/CsPb2Br5@SiO2 with the good water stability and high biocompatibility. These CsPbBr3/CsPb2Br5@SiO2 have been applied to construct FICT strips. To achieve the quantitative determination of human chorionic gonadotropin (HCG), a lab-made FICT strips detection system was established. The FICT strips had a good linear relationship to HCG in the range of 5–500 ng/mL, and the detection limit was 2.09 ng/mL. In addition, the recovery results of HCG detection in human urine samples also proved the feasibility of this FICT strips. CsPbBr3/CsPb2Br5@SiO2 can also be modified with different biomarkers for functionalization, which exhibits a promising application in the development of sensing platform of FICT strips.

Hybridization chain reaction assisted multicolor immunosensor for sensitively detection of human chorionic gonadotropin

The level of human chorionic gonadotropin (HCG) is an important indicator for early pregnancy, pregnancy-related diseases trophoblastic diseases and even cancer diagnosis. Therefore, sensitive detection of HCG has crucial significance in clinical, especially in gynaecology and obstetrics. Herein, a hybridization chain reaction (HCR) assisted multicolor immunosensor have been developed for HCG analysis. The proposed method introduced HCR after the immunoreaction between antibody and HCG protein, and produced long double strand DNA (dsDNA) that contain biotin sites. The streptavidin-horseradish peroxidase was linked on the dsDNA by the interaction between biotin and streptavidin, and can further mediated gold nanobipyramids (Au NBPs) etching. The localized surface plasmon resonance absorption peaks of Au NBPs blue shift and accompanied a vivid color change after etching effect. Based on this color change, HCG could be qualitative and semi-quantitative detected. Because of the introduction of HCR and enzyme amplification technique, the proposed method exhibited high sensitivity with a linear range of 0.1–2000 pg/mL and limit of detection (LOD) of 0.1 pg/mL. Finally, the proposed immunosensor was used to detect clinical serum samples. The results show there are no significant differences between clinical results and the test results by this method, indicating the practicability of the proposed method.

From Cereal Grains to Immunochemistry-What Role Have Antibodies Played in the History of the Home Pregnancy Test.

Today, the home pregnancy test is the most frequently performed laboratory test for self-diagnosis (home diagnostic test). It is also the first laboratory test that has been adapted for self-use at home. This is probably because women have always wanted to know the answer to the question: "Am I pregnant or not?" and always preferred to know the answer to this question intimately and in a discreet way. The history of the pregnancy test is also an interesting example of how the discovery of antibodies and the development of in vitro diagnostic methods based on the antigen-antibody reaction were important for the development of laboratory and clinical diagnostics. Immunodiagnostic techniques (based on the antigen-antibody reaction) are currently the basis of modern specialist laboratory diagnostics, which is essential in clinical diagnosis. The history of the pregnancy test is an interesting one and dates back to ancient times. A pregnancy test is defined as a procedure intended to reveal the presence or absence of pregnancy. Nowadays, every pregnancy test is based on the detection of human chorionic gonadotropin (hCG) in urine or blood. Human chorionic gonadotropin is secreted by the placenta right after a fertilized egg cell implants in the uterus and can be detected in both the urine and blood of pregnant women. Urine pregnancy tests are convenient for self-use at home. Blood tests are performed in medical laboratories. Specialized laboratory methods not only detect hCG but also determine the concentration of this hormone. However, both of these methods are highly accurate and common. Throughout the ages, many different methods were used to detect pregnancy at the earliest stage. Grain, wine, and various small animals were used as research tools. These were both long-term and often unreliable; most were based on folk beliefs and superstitions. Animal pregnancy tests were the first biological tests used in this field. This was a significant advance in the accurate detection of relatively early pregnancy. Animal tests in modern times are considered cruel and inhumane, no matter how reliable their results can be. Their place is now taken by much more specific, more sensitive, and definitely more ethical immunochemical tests. The pregnancy test and the methods to find out whether a woman is pregnant have gone through massive transformations, from bioassays using plants to bioassays on animals to advanced immunochemical techniques and biosensors. Modern pregnancy tests are not invasive and are very sensitive. Nowadays, it takes only about 3 min to know the answer to the question: "Am I pregnant or not?". However, it was not always as simple as it is today. This manuscript aims to show the important role played by antibodies in the development of laboratory and clinical diagnostics in the example of the interesting history of the pregnancy test.

Liquid crystal biosensor based on AuNPs signal amplification for detection of human chorionic gonadotropin

The detection of human chorionic gonadotropin (HCG) allows for the determination of pregnancy and is thus crucial during early pregnancy testing. This study introduces a novel liquid crystal (LC) biosensor that employs Au nanoparticles (AuNPs) for signal amplification, thus enabling the detection of the HCG antigen in a micro, efficient, and cost-effective manner. The sensor design capitalizes on the unique properties of LC to facilitate the detection of HCG. In this research, the surface of the base substrate was first modified with material from DMOAP and APTES, and EDC/sulfo-NHS was used to couple AuNPs and β-hCG to form an AuNP-β-hCG conjugate that improves the coupling rate. The carboxyl group of the antibody was reacted with the aldehyde group of glutaraldehyde, which helps to fix the β-hCG antibody to the surface of the substrate. The HCG sample is immobilized on the surface of the substrate via antigen-antibody immunobinding. As signal amplifiers, the AuNPs can have a significant effect on the topology of the interface and the vertical order of the LC molecules, thus reducing the limit of detection. Finally, the limit of detection was calculated using the SPSS system, and the relationship between grey values and concentrations was also obtained. The detection limit for HCG can be as low as 1.916 × 10−3 mIU·mL−1 under ideal conditions. Compared to other detection methods for HCG, this structure provides a detection pathway with excellent sensitivity, low detection limits, and better specificity, thus offering a new idea for HCG or any other target requiring trace detection.

Construction of a liquid crystal biosensor based on Fe3O4 nano-signal amplification and its application in HCG detection.

In this research, to improve the ability of nanomaterials to interfere with liquid crystal orientation, we constructed a novel liquid crystal biosensor using Fe3O4 nanospheres as signal amplifiers, which was used for the highly selective and sensitive detection of human chorionic gonadotropin (HCG). The Fe3O4 nanospheres in liquid crystal biosensors are still rare, in particular for the detection of the HCG antigen, a marker of pregnancy in women. This strategy takes advantage of the large spatial structure of Fe3O4 nanospheres to pre-immobilise β-hCG antibodies on the glass substrate, and, in the presence of HCG antigens, the antigen-antibody formed a specific immune response to disrupt the orientation of the liquid crystal. This allows an amplified optical signal to be generated for the ultimate successful detection of HCG antigen, and can greatly reduce the detectability of the target antigen concentration, ultimately greatly increasing the sensitivity of detection to a large degree. Thus, under optimal detection conditions, the minimum detection limit can be as low as 0.438 mIU mL-1. The prepared LC biosensor demonstrates excellent specificity and sensitivity compared to conventional nanomaterials used in liquid crystal biosensors, and will be of great benefit for future applications requiring trace detection of proteins, antibiotics, bacteria and so on, which is expected to provide a sensitive detection platform for HCG and other molecular monitors.

A novel test device and quantitative colorimetric method for the detection of human chorionic gonadotropin (hCG) based on Au@Zn-salen MOF for POCT applications.

The human chorionic gonadotropin (hCG) hormone is a biomarker that can predict tumors and early pregnancy; however, it is challenging to develop sensitive qualitative-quantitative procedures that are also effective, inventive, and unique. In this study, we used a novel easy in situ reaction of an organic nano-linker with Zn(NO3)2·6H2O and HAuCl4·3H2O to produce a gold-zinc-salen metal-organic framework composite known as Au-Zn-Sln-MOF. A wide variety of micro-analytical instruments and spectroscopic techniques were used in order to characterize the newly synthesized Au-Zn-Sln-MOF composite. Disclosure is provided for a novel swab test instrument and a straightforward colorimetric approach for detecting hCG hormone based on an Au-Zn-Sln-MOF composite. Both of these methods are easy. In order to validate a natural enzyme-free immunoassay, an Au-Zn-Sln-MOF composite was utilized in the role of an enzyme; a woman can use this gadget to determine whether or not she is pregnant in the early stages of the pregnancy or whether or not her hCG levels are excessively high, which is a symptom that she may have a tumor. This cotton swab test device is compatible with testing of various biological fluids, such as serum, plasma, or urine, and it can be easily transferred to the market to commercialize it as a costless kit, which will be 20-30% cheaper than what is available on the market. Additionally, it can be used easily at home and for near-patient testing (applications of point-of-care testing (POCT)).

Simple and Sensitive Electrochemical Sandwich-type Immunosensing of Human Chorionic Gonadotropin based on b-cyclodextrin Functionalized Graphene

The effective detection of human chorionic gonadotropin (HCG) is considerably important for the clinical diagnosis of both of early pregnancy and nonpregnancy-related diseases. In this work, a simple and sensitive electrochemical sandwich-type immunosensing platform was designed by synthesizing b-cyclodextrin (CD) functionalized graphene (CD/GN) hybrid as simultaneously sensing platform and signal transducer coupled with rhodamine b (RhB) as probe. In brief, GN offers large surface area and high conductivity, while CD exhibits superior host-guest recognition capability, thus the primary antibody (Ab1) of HCG can be bound into the cavities of CD/GN to form stable Ab1/CD/GN inclusion complex; meanwhile, the secondary antibody (Ab2) and RhB can also enter into the cavities, producing RhB/Ab2/CD/GN complex. Then, by using Ab1/ CD/GN as sensing platform and RhB/Ab2/CD/GN as signal transducer (in which RhB was signal probe), a simple sandwich-type immunosensor was constructed. Under the optimum parameters, the designed immunosensor exhibited a considerable low analytical detection of 1.0 pg mL&lt;sup&gt;−1&lt;/sup&gt; and a wide linearity of 0.002 to 10.0 ng mL&lt;sup&gt;−1&lt;/sup&gt; for HCG, revealing the developed sandwich-type electrochemical immunosensing platform offered potential real applications for the determination of HCG.

Enzyme Immunoassay for the Detection of Human Chorionic Gonadotropin (HCG) and Placental MRNA Marker a Practical Technique for Forensic Pregnancy Identification in Bloodstains

Introduction: The diagnosis of pregnancy from forensic bloodstains can be useful in cases of infanticide, criminal abortions and missing person identification. Objective: This research illustrated the use of a rapid, precise, and tremendously responsive enzyme immunoassay kit designed for medical usage, which is put to good use in our lab for qualitative HCG detection in blood stains and has proven to be a useful tool in forensic pregnancy identification. Methods: HCG concentrations had previously been generally known, and total eighty whole blood samples were taken: forty expectant females (every single one between months one to six of pregnancy), twenty healthy young males, and twenty postmenopausal females with good health ration has been cleared in all data. Results: Enzyme immunoassay is a useful forensic technique for detecting human chorionic gonadotropin hormone in pregnant women. In the forty sample batch that was dated for six months, 37 samples (92.5%) yielded positive results, 38 of which (95%) yielded good outcomes in the qualitative analysis, most of them within the sensitivities boundary. The samples that were diluted to 1/100 and 1/200 and kept at room temperature for one week and six months period, respectively, produced just two (5.0%) and five (12.5%) successful results and the samples showed negative results when diluted to 1/200 and stored for six months. Practical implication This paper reports on human chorionic gonadotropin (HCG) detection in bloodstains based on enzyme immunoassay. Conclusion: Enzyme immunoassay has proven to be a suitable method intended for detecting an hCG hormone in blood stains, allowing for the qualitative assessment of hCG, and making it particularly interesting for use in forensic science applications. Keywords: Enzyme immunoassay, human chorionic gonadotropin (hCG), pregnancy, bloodstain

Photoanode-supported cathodic immunosensor for sensitive and specific detection of human chorionic gonadotropin

Target biomarker detection with high accuracy in biological sample is necessary for the constructed immunoassays. Herein, a novel and enhanced cathodic immunosensor supported by photoanode was designed for sensitive and specific detection of human chorionic gonadotropin (HCG). Specifically, the electrode of TiO2 nanotube with N doping (TiO2:N) was fabricated and assembled with AgInS2 quantum dots (QDs) to acquire the TiO2:N/AgInS2 photoanode. For the sensing cathode, Pt nanoparticles (NPs) were decorated on carbon nanotubes (CNTs) to prepare the CNT/Pt cathodic matrix and was used to modify capture HCG antibody (Ab). In this photoelectrochemical (PEC) sensing system, the TiO2:N/AgInS2 photoanode served as the signal-converting element to produce prominent current signal, while the immune recognition events occurred on the sensing cathode to evidently change the initial current signal from steric hindrance effect. Profiting by excellent photoelectric property and good anti-interference ability of this featured PEC system, the developed cathodic immunosensor demonstrated high sensitivity and specificity for the detection of target HCG antigen (Ag). This photoanode-supported cathodic sensing strategy provided a potential path forward to exploit other enhanced PEC immunosensors in the application of biological samples.

An immunochromatography strip with peroxidase-mimicking ferric oxyhydroxide nanorods-mediated signal amplification and readout.

Immunochromatography testing strips (ICTs) promise to become the point-of-care test format for early diagnosis due to theirconvenience, low cost, and simplification. However, the insufficient signal intensity and limited sensitivity of this format hamper their application. Herein, we overcame these limitations by integrating rod-like ferric oxyhydroxide (β-FeOOH) nanoparticles with ICTs. Byvarying the concentration of PEI, a one-pot, mild-temperature hydrolysis method was adapted for the synthesis and morphology regulation of β-FeOOH nanorod. Due to the excellent enzyme-like catalytic activity toward peroxidase substrates (TMB) in the presence of hydrogen peroxide (H2O2), the β-FeOOH nanorod in ICTs served as a signal generator and thenanozyme for signal amplification. The proof-of-concept work was performed for the detection of human chorionic gonadotropin (hCG). Atwo fold improvement of detection sensitivity was achieved compared to the sensitivity of conventional Au NPs-based ICTs. These results show that β-FeOOH-based ICT has a potential application in POCT detection in clinical diagnostics.

The Application of the EP9-A Protocol in the Analysis of the Performance of the Immunofluorescence Assay for HCG Detection.

ObjectiveThe present study aims to evaluate the comparability of the results of two methodologies for detecting human chorionic gonadotropin (HCG) to assess whether the immunofluorescence method for detecting HCG is adequate for clinical applications.MethodsReferring to the protocol requirements of the American Clinical Laboratory Standards Institute (CLSI) EP9-A2 (methodological matching and bias assessment with patient samples), we collected 40 fresh serum specimens from our outpatients and inpatients, including 20 specimens with abnormal HCG concentrations (eight samples with different concentration ranges were selected daily and HCG was measured simultaneously with the two testing systems for five consecutive days). The assays were performed on a Dxl 800 fully automated immunoassay analyzer from Beckman Coulter Inc., USA, as a comparative method and on a Jet-iStar 3000 immunoassay analyzer from Zhonghan Shengtai Inc. as an experimental method. Methodological comparison and bias assessment of the results of the two methods for HCG detection were performed. The OLR regression model was used for calculating bias and regression analysis, and Spearman’s rank correlation coefficient was used for correlation analysis. The correlation and comparability of the two systems were calculated based on the results of the analysis.ResultsA good correlation in HCG results in the range of 5–50,000 U/mL was obtained from the two assay systems (r = 0.998) with the regression equation of y = 1.020x + 12.96. The estimated deviation was within the permissible deviation and acceptable.ConclusionThe results of HCG measurement by the two different assay systems were well correlated and comparable.

Modification of a nitrocellulose membrane with nanofibers for sensitivity enhancement in lateral flow test strips.

Lateral-flow analysis (LFA) is a convenient, low-cost, and rapid detection method, which has been widely used for screening of diseases. However, sensitivity enhancement in LFA is still a focus in this field and remains challenging. Herein, we propose an electrospinning coating method to modify the conventional nitrocellulose (NC) membrane and optimize the liquid flow rate for enhancing the sensitivity of the NC based LFA strips in the detection of human chorionic gonadotropin (HCG) and luteinizing hormone (LH). It can be seen that coating the NC membrane with nitrocellulose fibers could obtain a NC based strip with HCG and LH detection limits of 0.22 and 0.36 mIU mL−1 respectively, and a quantitative linear range of 0.5–500 mIU mL−1. The results show that electrospinning is effective in modifying conventional NC membranes for LFA applications.

Catalytic lateral flow immunoassays (cLFIA™): Amplified signal in a self-contained assay format

Lateral-flow immunoassays (LFIAs) are a widely used point-of-care technology because they are simple to perform and easy to read. LFIAs typically use colloidal gold or colored latex beads, however the sensitivity of LFIAs is ultimately limited by the label's extinction coefficients as enough material must be localized to be observed. Greater sensitivity requires visualization of fewer labels and herein we substitute palladium nanoparticles as a catalyst to produce a stable, blue indamine dye that precipitates at the capture line. We term our system cLFIA™ for catalytic LFIAs. The catalytic chemistry requires that three chemicals react with the palladium, and we have incorporate all three elements onto the cLFIA™ in the chemistry release fiber (CRF). With the CRF, cLFIA™ strips operate exactly as traditional LFIA strips, requiring no additional steps from the user, however the resulting lines are blue not red and provide much greater sensitivity. The all-in-one nature of cLFIA™ assays and the nature of the Pd conjugates we utilize sets this technology apart from other approaches that enhance LFIA sensitivity. We demonstrate that 2 nm Pd nanoparticles have a 40× catalytic advantage over 50 nm Pd-coated nanoparticles for our dye system. Our dye system is more robust than common peroxidase dyes (TMB), providing 8× signal and at a fast rate. Lastly, we demonstrate that the cLFIA™ approach is 1000× more sensitivity for detection of human chorionic gonadotropin than commercial pregnancy assays. The preparation of the palladium catalyst, the dye chemistry, and their facile use in cLFIA™ assays are described.

Gold nanoparticle-decorated metal organic frameworks on immunochromatographic assay for human chorionic gonadotropin detection.

Gold nanoparticle-decorated metal organic frameworks (MOF@AuNPs) with significantly enhanced color signal intensity were synthesized through in situ growth of AuNPs on the MOF skeleton. The resultant MOF@AuNP nanocomposites were characterized with 16.7-fold higher absorbance than conventional 40nm AuNPs (AuNP40). Thus, for the first time, we applied it as a signal amplification label to improve the immunochromatographic assay (ICA) of human chorionic gonadotropin (HCG). The detection limit of our enhanced ICA was 1.69 mIU/mL, which is ca. 10.6-fold improvement in sensitivity compared to traditional AuNP40-ICA. The recoveries of this MOF@AuNPs-ICA ranged from 86.03 to 119.22%, with coefficients of variation of 3.05 to 13.74%. The reliability and practicability were further validated by the clinically used chemiluminescence immunoassay method. Given their excellent signal amplification ability, the proposed MOF@AuNPs could serve as an ideal ICA label for rapid and sensitive detection of disease biomarkers. Graphical abstract.

Development of an experimental method to overcome the hook effect in sandwich-type lateral flow immunoassays guided by computational modelling

This study presents experimental demonstrations and theoretical underpinnings of how the high-analyte-concentration ‘hook effect’ in sandwich-type lateral flow immunoassays (LFIAs) may be overcome by real-time imaging of test and control lines. The dynamic range of a sandwich LFIA is limited by the ‘hook effect’, according to which, test line signal intensities reduce with increasing analyte concentration beyond a threshold analyte concentration. In order to understand the effect of analyte concentration on the kinetics of signal generation at the test and control lines, we developed a mathematical model of transport (convection and diffusion)-reaction phenomena occurring in these zones. Guided by the model, we developed a method for the expansion of the dynamic range of commercial unmodified LFIAs. The method involves time-lapse imaging of LFIA strips using a smartphone app and fitting the ratio of intensities at the test and control line (T/C ratio) to empirical equations. The fitting parameters thus obtained are calibrated against the analyte concentration. Using this method, the dynamic range for the detection of human chorionic gonadotropin (hCG) of an unmodified commercially available pregnancy strip was expanded to 3 orders of magnitude (0.5–500 IU/mL), compared to ∼2 orders of magnitude (0.5–40 IU/mL) achieved by end-point detection. Given the ubiquity of smartphones, this new quantitative method promises to significantly enhance the utility of LFIAs in point-of-care diagnostics.

Electrochemiluminescence immunoassay of human chorionic gonadotropin using silver carbon quantum dots and functionalized polymer nanospheres.

A composite, reduced graphene oxide (rGO) doped with silver nanoparticles (Ag NPs), was prepared by using binary reductants of sodium citrate and hydrazine hydrate. Carbon quantum dots (CQDs) synthesized by papaya peel combined with silver ions to form a CQDs-loaded silver nanoparticle (AgCQDs) nanocomposite. Polymer nanospheres (PNS) were generated via the infinite coordination polymer of ferrocene dicarboxylic acid and employed as carriers to load AgCQDs. The prepared AgCQDs@PNS-PEI has good biocompatibility and electrical conductivity and can be used as a matrix for the immobilization of a secondary antibody (Ab2). A sandwich-type electrochemiluminescence (ECL) immunosensor using AgCQDs@PNS-PEI nanocomposite as probe has been developed for the detection of human chorionic gonadotropin (HCG). The proposed immunosensor exhibits a linear range from 0.00100 to 500mIUmL-1 and the detection limit is 0.33μIUmL-1 (S/N = 3) under optimal conditions. The sensor exhibits excellent selectivity, good reproducibility, and high stability. These features demonstrate that the proposed method has promising potential for clinical protein detection and displays a new strategy to fabricate an immunosensor. Graphical abstract.

A smartphone-based rapid quantitative detection platform for lateral flow strip of human chorionic gonadotropin with optimized image algorithm

Colloidal gold immunochromatographic test strip has been widely used as a rapid, simple and low-cost correct detection technology. However, its detection is often qualitative or semi-quantitative, which limits its clinical application to some extent. Herein, a portable test strip quantitative detection device based on smartphone to detect human chorionic gonadotropin (HCG) is developed. In experiment, a colloidal gold HCG detection strip based on antigen antibody immune response is constructed, and the quantitative results of three different image processing methods on the same strip detection are compared, including the threshold processing algorithm based on location information, the RGB color component extraction algorithm and the grayscale projection value processing algorithm, the results show that the last algorithm can realize the best recognition of the region of interest of strip. The mobile phone application software (App) based on this design shows that the detection limit of constructed colloidal gold HCG strip is 3 ng/mL with a linear range of 6–300 ng/mL. The detection result of real urine sample is consistent with the spiked concentration (R2 = 0.988), indicating that the concentration of HCG can be accurately measured in urine with this method, presenting the potential for instant diagnosis.