Metal Affinity-Enabled Capture and Release Antibody Reagents Generate a Multiplex Biomarker Enrichment System that Improves Detection Limits of Rapid Diagnostic Tests

Magnetically Modulated Differential Quartz Crystal Microbalances for Rapid, Ultrasensitive, and Direct Probing of Prostate-Specific Antigens Conjugated with Magnetic Beads

The occurrence and development of diseases are closely related to overexpression of specific biomarkers in the serum of patients. Rapid and sensitive biomarker detection is beneficial for early diagnosis and treatment. However, the current laboratory processes and assays for biomarker detection are expensive and time-consuming, and their operation also requires a large number of professionals. We developed a magnetically modulated differential quartz crystal microbalance (MMD-QCM) method combined with magnetic bead (MB) labels for rapid and highly sensitive quantitative detection of prostate-specific antigen (PSA). Because MBs exhibit magnetized rotation motion under an applied AC magnetic field, a pair of QCMs are utilized to measure the difference between the magnetic motion intensities of the MBs and the MB-PSA immune complex to determine the PSA concentration. Experimental results demonstrate that the proposed method can be adopted to determine the PSA concentration in a wide range of 0.01-1000 ng/mL as well as exhibit a low detection limit of 0.065 ng/mL. In addition, the proposed scheme enables fast detection and low sample consumption. The single detection process takes less than 4 h and requires only 113 μL of sample solution. The proposed detection strategy is superior to the existing detection method and can be effectively used in early screening and prognostic diagnosis of cancer and other related diseases owing to its simplicity, low cost, and high speed.

Biosensors Based on the Binding Events of Nitrilotriacetic Acid-Metal Complexes

Molecular immobilization and recognition are two key events for the development of biosensors. The general ways for the immobilization and recognition of biomolecules include covalent coupling reactions and non-covalent interactions of antigen-antibody, aptamer-target, glycan-lectin, avidin-biotin and boronic acid-diol. Tetradentate nitrilotriacetic acid (NTA) is one of the most common commercial ligands for chelating metal ions. The NTA-metal complexes show high and specific affinity toward hexahistidine tags. Such metal complexes have been widely utilized in protein separation and immobilization for diagnostic applications since most of commercialized proteins have been integrated with hexahistidine tags by synthetic or recombinant techniques. This review focused on the development of biosensors with NTA-metal complexes as the binding units, mainly including surface plasmon resonance, electrochemistry, fluorescence, colorimetry, surface-enhanced Raman scattering spectroscopy, chemiluminescence and so on.

Characterization and utility of immobilized metal affinity-functionalized cellulose membranes for point-of-care malaria diagnostics

Immobilized metal affinity chromatography (IMAC) is a well-established technique for protein separation and purification. IMAC has been previously utilized to capture the malaria biomarker histidine-rich protein 2 (HRP2) from blood, enhancing the sensitivity of field-appropriate diagnostic tools such as lateral flow assays. However, little work has been done to translate this technique to a truly field-usable design. In this study, IMAC-functionalized cellulose membranes are created and characterized fully for future use in applied malaria diagnostics. IMAC-functionalized cellulose membranes were investigated across a range of cellulose substrates, IMAC ligands, and divalent transition metals before use in a capture and elution flowthrough workflow. Following characterization and optimization, it was found that iminodiacetic acid bound to Zn(II) was the most promising ligand-metal pair, with three available coordination sites and a molar loading capacity of 57.7 μmol of metal/cm³ of cellulose. Using these parameters, more than 99% of HRP2 was captured from a large-volume lysed blood sample in a simple flow-through assay and 89% of the captured protein was eluted from the membrane using the chelating compound ethylenediaminetetraacetic acid. Use of this enhancement protocol on an in-house HRP2 lateral flow assay (LFA) yielded a limit of detection of 7 parasites/μL, a 15.8x enhancement factor compared to traditional LFA methods.

Ultrasensitive fluorescence immunosensor based on mesoporous silica and magnetic nanoparticles: Capture and release strategy

Herein we designed a novel, highly sensitive, simple and amplified fluorescence immunosensing strategy for hepatitis B virus surface antigen (HBV surface antigen) (HBsAg) as a model based on the construction of a sandwich type probe. The operation mechanism of this immunosensing strategy is implemented by capturing and then stimulation-based-releasing of entrapped dye in the fluorescent capsules. The proposed probe is made by the Fe₃O₄ magnetic nanoparticle (Fe₃O₄ MNP) as a probe collector site and the Rhodamine B loaded-mesoporous silica nanoparticle (MSN-Rh.B) as a fluorescent mesoporous capsule and signal amplifier site. Such a methodology is benefited, from the advantages of the high ability of MSNs to be used as a scaffold for efficient dye encapsulation and the magnetic nanoparticles as efficient biological carriers. Under optimal conditions, the fluorescence signal (The fluorescence of solutions was measured using a quartz fluorescence cell (PMT voltage:720, Ex wavelegth:540, Em wavelength:568, All measurements were carried out at room temperature) increased with the increment of HBsAg concentration in the linear dynamic range of 6.1 ag/ml to 0.012 ng/ml with a detection limit (LOD) of 5.7 ag/ml. The relative standard deviation, measured between the resulting fluorescence peaks was obtained by 6.0%.

Inductively coupled plasma optical emission spectroscopy as a tool for evaluating lateral flow assays

Lateral flow assays (LFAs) are immunochromatographic point-of-care devices that have greatly impacted disease diagnosis through their rapid, inexpensive, and easy-to-use form factor. While LFAs have been successful as field-deployable tools, they have a relatively poor limit of detection when compared to more complex methods. Moreover, most design and manufacturing optimization is achieved through time- and resource-intensive brute-force optimization. Despite increased interests in LFA manufacturing, more quantitative tools are needed to study current manufacturing protocols and therefore, optimize and streamline development of these devices further. In this work, we focus on a critical LFA component, colloidal gold conjugated to a detection antibody, one of the most commonly used reporter elements. This study utilizes inductively coupled plasma optical emission spectroscopy (ICP-OES) in conjunction with a lateral flow reader to quantitatively analyze colloidal gold distributions at the read-out test and control lines, as well as residual gold on the conjugate pad and other flow through regions. Our goals are to develop a more rigorous understanding of current LFA designs as well as a quantitative understanding of shortcomings of operational characteristics for future improvement. To our knowledge, this is the first time that ICP-OES has been used to study the initial distribution of colloidal gold on an unused LFA and its redistribution after a test is performed. Using three different brands of commercially available malaria LFAs, gold content was measured within each section of an LFA at varying parasite test concentrations. As expected, the total mass of gold remained unchanged after LFA use; however, the total mass of initial gold and its redistribution varied among manufacturers. Importantly, there are also some inherent inefficiencies that exist in these commercial LFA designs; for example, only 30% of the total gold deposited onto Brand A LFAs binds to the test and control lines, sections of the test that contain interpretable signal. Using information gathered with this method, future devices could be more purposefully engineered to focus on improved binding efficiency, resulting in reduced costs, improved limit of detection, and diminished test-to-test and manufacturer-to-manufacturer variability.

An antibody-free dual-biomarker rapid enrichment workflow (AnDREW) improves the sensitivity of malaria rapid diagnostic tests

Rapid diagnostic tests (RDTs) are critical to the success of malaria elimination campaigns. These tests are rapid, user-friendly, and field-deployable to resource-limited regions. However, RDTs demonstrate poor sensitivity because they can only tolerate a small (5 μL) volume of blood, which limits the amount of protein biomarker delivered to the test. We have developed the Antibody-free Dual-biomarker Rapid Enrichment Workflow (AnDREW) for purifying histidine-rich protein 2 (HRP2) and Plasmodium lactate dehydrogenase (PLDH) from large volume (150 μL) blood samples. We used Zn(II)NTA and aptamer-conjugated magnetic beads to capture HRP2 and PLDH, respectively. Both biomarkers were then eluted into RDT-compatible volumes using ethylene diamine tetraacetic acid (EDTA). We optimized both bead conjugates individually by enzyme-linked immunosorbent assays (ELISAs) and then combined the optimized capture and elution assays for both biomarkers to produce the AnDREW. The AnDREW-enhanced RDTs exhibited a 11-fold and 9-fold improvement in analytical sensitivity for detection of HRP2 and PLDH, respectively, when compared to unenhanced RDTs. Moreover, the limit of detection for PLDH was improved 11-fold for the AnDREW-enhanced RDTs (3.80 parasites/μL) compared to unenhanced RDTs (42.31 parasites/μL). Importantly, the AnDREW utilizes a pan-specific PLDH aptamer and improves upon existing methods by eluting both biomarkers without complexed antibodies.

Exosome trapping and enrichment using a sound wave activated nano-sieve (SWANS)

Exosomes, a form of extracellular vesicle, are an important precursor in regenerative medicine. Microfluidic methods exist to capture these sub-micrometer sized objects from small quantities of sample, ideal for multiple diagnostic applications. To address the challenge of extraction from large volumes, we use the visual access offered by microfluidic techniques to probe the physical mechanisms behind a method which is compatible with future upscaling. The sound wave actuated nano-sieve uses resonant modes in a packed bed of microparticles to exert trapping forces on nanoparticles. Here, we examine the role of the microparticle size, demonstrating better performance from 15 μm particles than 7 μm particles. When applied to biological samples, we demonstrate for the first time that a packed bed of these larger particles is capable of capturing exosomes and liposomes, the captured particles being on average 20 to 40 times smaller than the pores within the trapped bed.

Sound wave activated nano-sieve (SWANS) for enrichment of nanoparticles

Acoustic actuation is widely used in microfluidic systems as a method of controlling the behaviour of suspended matter. When acoustic waves impinge on particles, a radiation force is exerted which can cause migration over multiple acoustic time periods; in addition the scattering of the wave by the particle will affect the behaviour of nearby particles. This interparticle effect, or Bjerknes force, tends to attract particles together. Here, instead of manipulating a dilute sample of particles, we examine the acoustic excitation of a packed bed. We fill a microfluidic channel with microparticles, such that they form a closely packed structure and then excite them at the particle's resonant frequency. In this scenario, each particle acts as a source of scattered waves and we show that these waves are highly effective at attracting nanoparticles onto the surface of the microparticles, and nanoparticle collection characterises the performance of this mechanically activated packed bed.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

Plasmonic molecular assays: Recent advances and applications for mobile health

Plasmonics-based biosensing assays have been extensively employed for biomedical applications. Significant advancements in use of plasmonic assays for the construction of point-of-care (POC) diagnostic methods have been made to provide effective and urgent health care of patients, especially in resourcelimited settings. This rapidly progressive research area, centered on the unique surface plasmon resonance (SPR) properties of metallic nanostructures with exceptional absorption and scattering abilities, has greatly facilitated the development of cost-effective, sensitive, and rapid strategies for disease diagnostics and improving patient healthcare in both developed and developing worlds. This review highlights the recent advances and applications of plasmonic technologies for highly sensitive protein and nucleic acid biomarker detection. In particular, we focus on the implementation and penetration of various plasmonic technologies in conventional molecular diagnostic assays, and discuss how such modification has resulted in simpler, faster, and more sensitive alternatives that are suited for point-of-use. Finally, integration of plasmonic molecular assays with various portable POC platforms for mobile health applications are highlighted.