Application of a microfluidic paper-based bioimmunosensor with laser-induced fluorescence detection in the determination of alpha-fetoprotein from serum of hepatopaths

Laser-printed paper ELISA and hydroxyapatite immobilization for colorimetric congenital anomalies screening in saliva

BACKGROUND

Alpha-fetoprotein (AFP) is a fetal protein that can indicate congenital anomalies such as Down syndrome and spinal canal blockage when detected at abnormal levels in pregnant women. Current AFP detection methods rely on invasive blood or serum samples, which require sophisticated equipment. From the many solutions proposed, colorimetric paper-based assays excel in point-of-care settings. The concept of paper-based ELISA (p-ELISA) enhances traditional methods, aligning with the ASSURED criteria for diagnostics in resource-limited regions. Despite success in microfluidic paper-based assay devices, laser printing remains underexplored for p-ELISA. Additionally, modifying the paper surface provides an additional layer of sensitivity enhancement.

RESULTS

In this study, we developed a novel laser-printed paper-based ELISA (LP-pELISA) for rapid, sensitive, and noninvasive detection of AFP in saliva samples. The LP-pELISA platform was fabricated by printing hydrophobic barriers on filter paper using a laser printer, followed by depositing hydroxyapatite (HAp) as an immobilization material for the antibodies. The colorimetric detection was achieved using AuNPs functionalized with anti-AFP antibodies and silver nitrate enhancement. The LP-pELISA exhibited a linear response for AFP detection in both buffer and saliva samples over a range of 1.0-800 ng mL-1, with a limit of detection (LOD) reaching 1.0 ng mL-1. The assay also demonstrated good selectivity, repeatability, reproducibility, and stability. The LP-pELISA was further validated by testing spiked human saliva samples, showing its potential for point-of-care diagnosis of congenital disabilities.

SIGNIFICANCE

The LP-pELISA is a noninvasive platform showcasing simplicity, cost-effectiveness, and user-friendliness, utilizing laser printing, hydroxyapatite modification, and saliva samples to efficiently detect AFP. Beyond its application for AFP, this method's versatility extends to other biomarkers, positioning it as a catalyst for the evolution of paper-based biosensors. The LP-pELISA holds promise as a transformative tool for point-of-care diagnostics, fostering advancements in healthcare with its innovative technology.

Advances in Microfluidic Paper-Based Analytical Devices (µPADs): Design, Fabrication, and Applications

Microfluidic Paper-based Analytical Devices (µPADs) have emerged as a new class of microfluidic systems, offering numerous advantages over traditional microfluidic chips. These advantages include simplicity, cost-effectiveness, stability, storability, disposability, and portability. As a result, various designs for different types of assays are developed and investigated. In recent years, µPADs are combined with conventional detection methods to enable rapid on-site detection, providing results comparable to expensive and sophisticated large-scale testing methods that require more time and skilled personnel. The application of µPAD techniques is extensive in environmental quality control/analysis, clinical diagnosis, and food safety testing, paving the way for on-site real-time diagnosis as a promising future development. This review focuses on the recent research advancements in the design, fabrication, material selection, and detection methods of µPADs. It provides a comprehensive understanding of their principles of operation, applications, and future development prospects.

A compact microfluidic laser-induced fluorescence immunoassay system using avalanche photodiode for rapid detection of alpha-fetoprotein

Alpha-fetoprotein (AFP), commonly employed for early diagnosis of liver cancer, serves as a biomarker for cancer screening and diagnosis. Combining the high sensitivity and specificity of fluorescence immunoassay (FIA), developing a low-cost and efficient immunoassay system for AFP detection holds significant importance in disease diagnosis. In this work, we developed a miniaturized oblique laser-induced fluorescence (LIF) immunoassay system, coupled with a microfluidic PMMA/paper hybrid chip, for rapid detection of AFP. The system employed an avalanche photodiode (APD) as the detector, and implemented multi-level filtering in the excitation light channel using the dichroic mirror and optical trap. At first, we employed the Savitzky-Golay filter and baseline off-set elimination methods to denoise and normalize the original data. Then the cutoff frequency of the low-pass filter and the reverse voltage of the APD were optimized to enhance the detection sensitivity of the system. Furthermore, the effect of laser power on the fluorescence excitation efficiency was investigated, and the sampling time during the scanning process was optimized. Finally, a four-parameter logistic (4PL) model was utilized to establish the concentration-response equation for AFP. The system was capable of detecting concentrations of AFP standard solution within the range of 1-500 ng/mL, with a detection limit of 0.8 ng/mL. The entire immunoassay process could be completed within 15 min. It has an excellent potential for applications in low-cost portable diagnostic instruments for the rapid detection of biomarkers.

Biomarker Detection in Early Diagnosis of Cancer: Recent Achievements in Point-of-Care Devices Based on Paper Microfluidics

Microfluidics is very crucial in lab-on-a-chip systems for carrying out operations in a large-scale laboratory environment on a single chip. Microfluidic systems are miniaturized devices in which the fluid behavior and control can be manipulated on a small platform, with surface forces on the platform being greater than volumetric forces depending on the test method used. In recent years, paper-based microfluidic analytical devices (μPADs) have been developed to be used in point-of-care (POC) technologies. μPADs have numerous advantages, including ease of use, low cost, capillary action liquid transfer without the need for power, the ability to store reagents in active form in the fiber network, and the capability to perform multiple tests using various measurement techniques. These benefits are critical in the advancement of paper-based microfluidics in the fields of disease diagnosis, drug application, and environment and food safety. Cancer is one of the most critical diseases for early detection all around the world. Detecting cancer-specific biomarkers provides significant data for both early diagnosis and controlling the disease progression. μPADs for cancer biomarker detection hold great promise for improving cure rates, quality of life, and minimizing treatment costs. Although various types of bioanalytical platforms are available for the detection of cancer biomarkers, there are limited studies and critical reviews on paper-based microfluidic platforms in the literature. Hence, this article aims to draw attention to these gaps in the literature as well as the features that future platforms should have.

Microfluidic-based blood immunoassays

Microfluidics enables the integration of whole protocols performed in a laboratory, including sample loading, reaction, extraction, and measurement steps on a single system, which offers significant advantages thanks to small-scale operation combined with precise fluid control. These include providing efficient transportation mechanisms and immobilization, reduced sample and reagent volumes, fast analysis and response times, lower power requirements, lower cost and disposability, improved portability and sensitivity, and greater integration and automation capability. Immunoassay is a specific bioanalytical method based on the interaction of antigens and antibodies, which is utilized to detect bacteria, viruses, proteins, and small molecules in several areas such as biopharmaceutical analysis, environmental analysis, food safety, and clinical diagnostics. Because of the advantages of both techniques, the combination of immunoassays and microfluidic technology is considered one of the most potential biosensor systems for blood samples. This review presents the current progress and important developments in microfluidic-based blood immunoassays. After providing several basic information about blood analysis, immunoassays, and microfluidics, the review points out in-depth information about microfluidic platforms, detection techniques, and commercial microfluidic blood immunoassay platforms. In conclusion, some thoughts and future perspectives are provided.

Circulating Biomarkers for the Early Diagnosis and Management of Hepatocellular Carcinoma with Potential Application in Resource-Limited Settings

Hepatocellular carcinoma (HCC) is among the world's third most lethal cancers. In resource-limited settings (RLS), up to 70% of HCCs are diagnosed with limited curative treatments at an advanced symptomatic stage. Even when HCC is detected early and resection surgery is offered, the post-operative recurrence rate after resection exceeds 70% in five years, of which about 50% occur within two years of surgery. There are no specific biomarkers addressing the surveillance of HCC recurrence due to the limited sensitivity of the available methods. The primary goal in the early diagnosis and management of HCC is to cure disease and improve survival, respectively. Circulating biomarkers can be used as screening, diagnostic, prognostic, and predictive biomarkers to achieve the primary goal of HCC. In this review, we highlighted key circulating blood- or urine-based HCC biomarkers and considered their potential applications in resource-limited settings, where the unmet medical needs of HCC are disproportionately highly significant.

Rapid identification and quantitation of single plant seed allergen using paper-based microfluidics

Nucleic acid amplification is a sensitive and powerful tool for allergen detection. However, it is limited due to the relatively cumbersome methods required to extract nucleic acids from single plant seed allergen (e.g. peanut and soybean). In view of this, an approach of extracting nucleic acid with untreated glass-fiber paper (paper-based microfluidics) was applied for nucleic acid capture and purification from plant seed allergen and commercial products. After cut by hollow cylindrical cutter, a certain size the paper chip it used to absorb DNA. And this paper-based microfluidics with DNA was directly applied for amplification by loop-mediated isothermal amplification (LAMP). To evaluate the adsorption performance of paper chip to DNA, CTAB and SDS method were used as comparisons. From amplification results, the established technique has good specificity, high repeatability (C.V. values are 4.41% and 6.17% for peanut and soybean) and favorable sensitivity (7.39 ng/μL or peanut and 6.6 ng/μL for soybean), and successfully used for commercial products (2 kinds of candy and 2 kinds of cakes containing peanut, and 2 kinds of drinks, candy and 2 kinds of biscuits containing soybean). This speed and flexible detection method makes it suit for applications in point-of-care (POC) detection at different scenario, such as custom house and import port.

Auto-fluorescence of cellulose paper with spatial solid phrase dispersion-induced fluorescence enhancement behavior for three heavy metal ions detection

Auto-fluorescence of cellulose paper is often considered as an interfering fluorescence, which directly impedes the cellulose paper as a substrate material. This paper creatively explored the composition and properties of auto-fluorescence, and lignosulfonate was primarily speculated as the main source of auto-fluorescence. Surprisingly, its spatial solid phrase dispersion-induced fluorescence enhancement behavior was found. Then, cellulose paper was modified with Mn-doped ZnS quantum dots, and the prepared ratiometric fluorescent paper chip has good performances on morphology, stability, and fluorescence properties. Besides, the paper chip exhibited different fluorescence responses to three heavy metal ions in water sample. The limit of detection for Cd²⁺, Hg²⁺ and Pb²⁺ reached 1.61 nM, 0.01 nM, and 0.02 nM, respectively. In short, the molecular simulation results theoretically proved that heavy metal ions owned substitution affinity with lignosulfonate. Ultimately, this study was the first attempt to utilize paper-based auto-fluorescence, which could better accelerate the development of paper-based chips.

Micro-/nano-fluidic devices and in vivo fluorescence imaging based on quantum dots for cytologic diagnosis

Semiconductor quantum dots (QDs) possess attractive merits over traditional organic dyes, such as tunable emission, narrow emission spectra and good resistance against optical bleaching, and play a vital role in biosensing and bioimaging for cytologic diagnoses. Microfluidic technology is a potentially useful strategy, as it provides a rapid platform for tracing of disease markers. In vivo fluorescence imaging (FI) based on QDs has become popular for the analysis of complex biological processes. We herein report the applications of multifunctional fluorescent QDs as sensitive probes for diagnoses on cancer medicine and stem cell therapy via microfluidic chips and in vivo imaging.

Hand-Operated, Paper-Based Rotational Vertical-Flow Immunosensor for the Impedimetric Detection of α-Fetoprotein

This study demonstrates a hand-operated, paper-based rotational vertical-flow immunosensor (rotational VFI) platform requiring fewer pipetting steps, designed for the electrochemical detection of α-fetoprotein with multiple and time-sequenced steps. The platform allows users to perform electrochemical measurements without interference from the convective component of fluid motion, which is unfavorable in most techniques. Users can freely transfer-switch-stop fluid flows by manually rotating the paper disk, evidencing the superior flexibility of this sensor compared to other biosensors. Furthermore, the overall assay duration can be considerably shortened to 9 min. The linear range (LR) is determined to be 0.01-500 ng/mL, with a limit of detection (LOD) of 1.65 pg/mL, and the sensitivity can be significantly enhanced simply by switching off the sample stream to ensure detention at the binding zone (for up to 30 min). This additional step can widen the LR to 0.5 pg/mL, with a LOD of 3.54 fg/mL, which is the lowest detectable level ever reported among paper-based sensors. The advantages of the designed rotational VFI qualify it as a suitable alternative to various biosensors.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Recent Progress in DNA Hybridization Chain Reaction Strategies for Amplified Biosensing

With the continuous development of DNA nanotechnology, various spatial DNA structures and assembly techniques emerge. Hybridization chain reaction (HCR) is a typical example with exciting features and bright prospects in biosensing, which has been intensively investigated in the past decade. In this Spotlight on Applications, we summarize the assembly principles of conventional HCR and some novel forms of linear/nonlinear HCR. With advantages like great assembly kinetics, facile operation, and an enzyme-free and isothermal reaction, these strategies can be integrated with most mainstream reporters (e.g., fluorescence, electrochemistry, and colorimetry) for the ultrasensitive detection of abundant targets. Particularly, we select several representative studies to better illustrate the novel ideas and performances of HCR strategies. Theoretical and practical utilities are confirmed for a range of biosensing applications. In the end, a deep discussion is provided about the challenges and future tasks of this field.

One-sampling and Rapid Analysis of Cancer Biomarker on A Power-free and Low-cost Microfluidic Chip

Alpha-fetoprotein (AFP) is an important disease biomarker, relating to cancers such as hepatocarcinomas and gastric cancer. However, traditional methods are time-consuming, relied on bulky instruments and trained professionals, cannot satisfy the demand for low cost and point-of-care testing (POCT). In this study, a power-free POCT device was developed for the rapid and low-cost detection of AFP via one-sampling. Based on the principle of sandwich immunofluorescence, the chip is capable of automatically accomplishing on-chip mixing, labeling and capturing procedures, which only require that operator add 40 μL sample into the chip one time. The proposed device is capable of sensitively detecting human AFP in FBS with a dynamic range of 10 - 1000 ng/mL and LOD (1.88 ng/mL) within a short time of 3 min. Predictably, our method holds a great potential to be applied in the POC diagnostics of proteins, especially for some regions that are resource-limited.