Apoferritin protein nanoparticles dually labeled with aptamer and horseradish peroxidase as a sensing probe for thrombin detection

Sandwich-type aptamer-based biosensors for thrombin detection

Thrombin, a proteolytic enzyme, plays an essential role in catalyzing many blood clotting reactions. Thrombin can act as a marker for some blood-related diseases, such as leukemia, thrombosis, Alzheimer's disease and liver disease. Therefore, its diagnosis is of great importance in the fields of biological and medical research. Biosensors containing sandwich-type structures have attracted much consideration owing to their superior features such as reproducible and stable responses with easy improvement in the sensitivity of detection. Sandwich-type platforms can be designed using a pair of receptors that are able to bind to diverse locations of the same target. Herein, we investigate recent advances in the progress and applications of thrombin aptasensors containing a sandwich-type structure, in which two thrombin-binding aptamers (TBAs) identify different parts of the thrombin molecule, leading to the formation of a sandwich structure and ultimately signal detection. We also discuss the pros and cons of these approaches and outline the most logical approach in each section.

Enhanced Electrochemical Characterization of the Immune Checkpoint Protein PD-L1 using Aptamer-Functionalized Magnetic Metal-Organic Frameworks

Programmed death ligand 1 (PD-L1) is highly expressed in cancer cells and participates in the immune escape process of tumor cells. However, as one of the most promising biomarkers for cancer immunotherapy monitoring, the key problem ahead of practical usage is how to effectively improve the detection sensitivity of PD-L1. Herein, an electrochemical aptasensor for the evaluation of tumor immunotherapy is developed based on the immune checkpoint protein PD-L1. The fundamental principle of this method involves the utilization of DNA nanotetrahedron (NTH)-based capture probes and aptamer-modified magnetic metal-organic framework nanocomposites as signaling probes. A synergistic enhancement is observed in the electrocatalytic effect between Fe3O4 and UiO-66 porous shells in Fe3O4@UiO-66 nanocomposites. Therefore, the integration of aptamer-modified Fe3O4@UiO-66@Au with NTH-assisted target immobilization as an electrochemical sensing platform can significantly enhance sensitivity and specificity for target detection. This method enables the detection of targets at concentrations as low as 7.76 pg mL-1 over a wide linear range (0.01 to 1000 ng mL-1). The authors have successfully employed this sensor for in situ characterization of PD-L1 on the cell surface and for monitoring changes in PD-L1 expression during drug therapy, providing a cost-effective yet robust alternative to highly expensive and expertise-dependent flow cytometry.

An electrochemical aptasensor for detection of prostate-specific antigen using reduced graphene gold nanocomposite and Cu/carbon quantum dots

We report a label-free electrochemical aptamer-based biosensor for the detection of human prostate-specific antigen (PSA). The thiolate DNA aptamer against PSA was conjugated to the reduced graphene oxide/Au (RGO-Au) nanocomposite through the self-assembly of Au-S groups. Owing to the large volume to surface ratio, the RGO-Au nanocomposite provides a large surface for aptamer loading. The RGO-Au/aptamer was combined with a Nafion polymer and immobilized on a glassy carbon electrode. The interaction of aptamer with PSA was studied by cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The detection of limit for prepared electrode was obtained about 50 pg/mL at the potential of 0.4 V in potassium hexacyanoferrate [K₄ Fe(CN)₆ ] medium. To decrease the limit of detection (LOD) and applied potential of the prepared nanoprobe Cu/carbon quantum dots (CuCQD) is introduced as a new redox. The results show that this new electrochemical medium provides better conditions for the detection of PSA. LOD of a nanoprobe in CuCQD media was obtained as 40 pg/mL at the potential of -0.2 V. Under optimal conditions, the aptasensor exhibits a linear response to PSA with a LOD as small as 3 pg/mL. The present aptasensor is highly selective and sensitive and shows satisfactory stability and repeatability.

Ferritin-catalyzed synthesis of ferrihydrite nanoparticles with high mimetic peroxidase activity for biomolecule detection

Natural enzymes are generally sophisticated structural proteins that catalyze biological reactions with high specificity and efficiency and thus offer great potential in various disciplines, but intrinsic proteinic features such as easy denaturation and digestion restrict their practical application. So far, many functional nanomaterials with robust structures have been advanced as enzyme-mimetic catalysts to replace natural enzymes, however, their synthesis processes are generally complicated and require harsh experimental conditions such as high temperature and pressure. Herein, we report the facile synthesis of nanoparticles with high peroxidase-like activity by enzymatic catalysis. Specifically, by utilizing the intrinsic ferroxidase activity and mineralization capability of ferritin, ferrihydrite nanoparticles can be easily prepared within the apoferritin cavity at room temperature in aqueous solution (pH ∼ 7.0). Notably, reconstituted ferrihydrite nanoparticles exhibited comparative catalytic activity with a natural enzyme, horse radish peroxidase. Notably, when coupled with another oxidase, a dual-enzyme sensor system can be constructed for the detection of biomolecules such as glucose, and xanthine. Due to the biocompatibility and easy modification of the ferritin shell using well-established chemical and genetic techniques, the nanoparticles encapsulated by a protein shell possess great potential application in theranostics and immunoassays.

Functional Nucleic Acid Nanomaterials: Development, Properties, and Applications

Functional nucleic acid (FNA) nanotechnology is an interdisciplinary field between nucleic acid biochemistry and nanotechnology that focuses on the study of interactions between FNAs and nanomaterials and explores the particular advantages and applications of FNA nanomaterials. With the goal of building the next-generation biomaterials that combine the advantages of FNAs and nanomaterials, the interactions between FNAs and nanomaterials as well as FNA self-assembly technologies have established themselves as hot research areas, where the target recognition, response, and self-assembly ability, combined with the plasmon properties, stability, stimuli-response, and delivery potential of various nanomaterials can give rise to a variety of novel fascinating applications. As research on the structural and functional group features of FNAs and nanomaterials rapidly develops, many laboratories have reported numerous methods to construct FNA nanomaterials. In this Review, we first introduce some widely used FNAs and nanomaterials along with their classification, structure, and application features. Then we discuss the most successful methods employing FNAs and nanomaterials as elements for creating advanced FNA nanomaterials. Finally, we review the extensive applications of FNA nanomaterials in bioimaging, biosensing, biomedicine, and other important fields, with their own advantages and drawbacks, and provide our perspective about the issues and developing trends in FNA nanotechnology.

Multiplexed electrochemical aptasensor for antibiotics detection using metallic-encoded apoferritin probes and double stirring bars-assisted target recycling for signal amplification

Simultaneous and sensitive detection of various antibiotic residues in one sample is essential to evaluation of food safety status. Herein, a multiplexed electrochemical aptasensor for multiplex antibiotics detection, with kanamycin (KANA) and ampicillin (AMP) as representative analytes, was designed by using metal ions encoded apoferrtin probes and double stirring bars-assisted target recycling for signal amplification. The encoded probes were prepared by apoferritin loading Cd²⁺ and Pb²⁺ ions and labeling with duplex DNAs (aptamers corresponding to KANA and AMP hybrid with its complementary DNA sequence), respectively. In the presence of KANA and AMP, the targets can recurrently react with the probes on the bars, and then replace a lot of Apo-Mencoded signal tags into supernatant. The peak currents of Cd²⁺and Pb²⁺from the tags corresponding with the concentrations of KANA and AMP were detected by square wave voltammetry in one run. As a result, KANA and AMP can be detected simultaneously within the range from 0.05 pM to 50 nM. And the detection limits were 18 fM KANA and 15 fM AMP (S/N = 3). The assay was testified to detect KANA and AMP residues with consistent results of ELISA in samples, e.g. milks and fishes. The assay was highly-sensitive, selective, cost-effective and easy-to-operate due to Apo-M encoded probes with high loading capacity of signal source substances. Moreover, double stirring bar-assisted target recycling, which was enzyme-free and could overcome matrix interference, was fabricated for signal amplification. Thus, the assay showed potential advantages for sensitively screening of antibiotic residues in foods.

Development and characterization of folic acid-functionalized apoferritin as a delivery vehicle for epirubicin against MCF-7 breast cancer cells

Epirubicin (Epr) is an effective chemotherapeutic drug; however, the clinical amenability of Epr is limited by its highly toxic interaction with normal cells. This toxicity can be decreased by utilizing nanocarriers and targeted drug delivery systems. This work describes an approach for the delivery of Epr via encapsulation in the horse spleen apoferritin (HsAFr) cavity. The encapsulation was achieved by the disassembling of apoferritin into subunits at pH 2 followed by its reformation at pH 7.4 in the presence of Epr. The surface of HsAFr-encapsulated Epr was modified with folic acid (FA) for optimal targeting of breast cancer cells (MCF-7). The use of FA to functionalize HsAFr could enhance the cellular uptake efficiency via FA-receptor-mediated endocytosis. UV-vis spectroscopy, fluorescence spectroscopy, circular dichroism (CD) and transmission electron microscopy (TEM) were utilized for structural characterization of the HsAFr-Epr and HsAFr-Epr-FA complexes. The comparison of the anti-cancer activities across the HsAFr-Epr-FA complex and the free Epr drug was performed using the MTT viability assay on MCF-7.

A new electrochemical aptasensor for sensitive assay of a protein based on the dual-signaling electrochemical ratiometric method and DNA walker strategy

Herein, a new electrochemical aptamer-based biosensor for highly sensitive assay of thrombin has been developed based on the dual-signaling electrochemical ratiometric method and the DNA walker strategy, and shows a low detection limit of about 56 fM.

Functional ferritin nanoparticles for biomedical applications

Ferritin, a major iron storage protein with a hollow interior cavity, has been reported recently to play many important roles in biomedical and bioengineering applications. Owing to the unique architecture and surface properties, ferritin nanoparticles offer favorable characteristics and can be either genetically or chemically modified to impart functionalities to their surfaces, and therapeutics or probes can be encapsulated in their interiors by controlled and reversible assembly/disassembly. There has been an outburst of interest regarding the employment of functional ferritin nanoparticles in nanomedicine. This review will highlight the recent advances in ferritin nanoparticles for drug delivery, bioassay, and molecular imaging with a particular focus on their biomedical applications.

ABCs of DNA aptamer and related assay development

This review is intended to guide the novice in aptamer research and development to understand virtually all of the aptamer development options and currently available assay modalities. Aptamer development topics range from discussions of basic and advanced versions of Systematic Evolution of Ligands by EXponential Enrichment (SELEX) and SELEX variations involving incorporation of exotic unnatural nucleotides to expand library diversity for even greater aptamer affinity and specificity to improved next generation methods of DNA sequencing, screening and tracking aptamer development throughout the SELEX process and characterization of lead aptamer candidates. Aptamer assay development topics include descriptions of various colorimetric and fluorescent assays in microplates or on membranes including homogeneous beacon and multiplexed Fluorescence Resonance Energy Transfer (FRET) assays. Finally, a discussion of the potential for marketing successful aptamer-based assays or test kits is included.

Ultrasensitive electrochemical aptasensor based on sandwich architecture for selective label-free detection of colorectal cancer (CT26) cells

Colorectal cancer is one of the most common cancers in the world and has no effective treatment. Therefore, development of new methods for early diagnosis is instantly required. Biological recognition probes such as synthetic receptor and aptamer is one of the candidate recognition layers to detect important biomolecules. In this work, an electrochemical aptasensor was developed by fabricating an aptamer-cell-aptamer sandwich architecture on an SBA-15-3-aminopropyltriethoxysilane (SBA-15-pr-NH₂) and Au nanoparticles (AuNPs) modified graphite screen printed electrode (GSPE) surface for the selective, label-free detection of CT26 cancer cells. Based on the incubation of the thiolated aptamer with CT26 cells, the electron-transfer resistance of Fe (CN)₆^3-/4- redox couple increased considerably on the aptasensor surface. The results obtained from cyclic voltammetry and electrochemical impedance spectroscopy studies showed that the fabricated aptasensor can specifically identify CT26 cells in the concentration ranges of 10-1.0×10⁵cells/mL and 1.0×10⁵-6.0×10⁶ cells/mL, respectively, with a detection limit of 2cells/mL. Applying the thiol terminated aptamer (5TR1) as a recognition layer led to a sensor with high affinity for CT26 cancer cells, compared to control cancer cells of AGS cells, VERO Cells, PC3 cells and SKOV-3 cells. Therefore a simple, rapid, label free, inexpensive, excellent, sensitive and selective electrochemical aptasensor based on sandwich architecture was developed for detection of CT26 Cells.

Sensitive detection of bisphenol A based on a ratiometric electrochemical aptasensor

A new ratiometric electrochemical aptasensor has been developed for highly sensitive and selective detection of bisphenol A (BPA). The double-stranded DNA (dsDNA), consisting of the BPA aptamer (DNA1) and methylene blue (MB)-labeled complementary DNA (cDNA), was immobilized on a gold nanoparticle (AuNP) modified glassy carbon (GC) electrode. In the presence of BPA, the specific BPA–aptamer interaction drove the release of the MB-labeled cDNA from the electrode surface. As a result, the oxidation peak current of MB (IMB) decreased and that of BPA (IBPA) increased. The peak current ratio (IBPA/IMB) of BPA and MB was linear with the concentration of BPA in the range from 1 to 100 pmol/L with a detection limit of 0.6 pmol/L. The detection limit is much lower than that obtained by most of the reported electrochemical methods. On the other hand, the developed aptasensor possesses good selectivity, reproducibility, and stability, and the related sensing structure is very simple, showing promising practical applications in BPA assays.

Apoferritin applications in nanomedicine

Nanomedicine as a continuously evolving discipline is still looking for a structure with perfect properties that is usable as a multifunctional transporter. Great potential is attributed to synthetic materials such as fullerenes, porous hollow silica nanoparticles and single-wall nanotubes, among others. However, materials that are natural to the human body are more acceptable by the organism, and thus become an attractive approach in this field of research. Ferritins are proteins that naturally occur in most living organisms throughout evolution and may be a possible transporter choice. Numerous applications have demonstrated the possibilities of iron-free ferritins, called apoferritins, serving as platforms for various nanomedical purposes This article summarizes the advantages and disadvantages of these proteins and discusses their practical applications and future perspectives.

A simple strategy for signal amplification based on DNA hybridization chain reaction for thrombin detection

Multiple enzymes were introduced onto the surface of electrode, which resulted in significant signal amplification.

Plasma-Enabled Carbon Nanostructures for Early Diagnosis of Neurodegenerative Diseases

Carbon nanostructures (CNs) are amongst the most promising biorecognition nanomaterials due to their unprecedented optical, electrical and structural properties. As such, CNs may be harnessed to tackle the detrimental public health and socio-economic adversities associated with neurodegenerative diseases (NDs). In particular, CNs may be tailored for a specific determination of biomarkers indicative of NDs. However, the realization of such a biosensor represents a significant technological challenge in the uniform fabrication of CNs with outstanding qualities in order to facilitate a highly-sensitive detection of biomarkers suspended in complex biological environments. Notably, the versatility of plasma-based techniques for the synthesis and surface modification of CNs may be embraced to optimize the biorecognition performance and capabilities. This review surveys the recent advances in CN-based biosensors, and highlights the benefits of plasma-processing techniques to enable, enhance, and tailor the performance and optimize the fabrication of CNs, towards the construction of biosensors with unparalleled performance for the early diagnosis of NDs, via a plethora of energy-efficient, environmentally-benign, and inexpensive approaches.

A simple label-free electrochemical aptasensor for dopamine detection

A simple and label-free electrochemical biosensor based on a dopamine DNA aptamer was developed for the sensitive and selective detection of dopamine.

Sensitive electrochemical aptasensor by coupling "signal-on'' and "signal-off'' strategies

A simple electrochemical aptasensor for sensitive and selective determination of adenosine triphosphate (ATP) has been developed on the basis of a new dual-signaling amplification strategy. This aptasensor features both ''signal-on'' and ''signal-off'' elements. The ferrocene (Fc)-labeled aptamer probe (Fc-P) is designed to hybridize with the thiolated methylene blue (MB)-modified DNA probe (MB-P) on gold electrode to form rigid duplex DNA. In the presence of ATP, the interaction between ATP and the aptamer leads to the dissociation of the duplex DNA structure and thereby the release of the Fc-P from the sensing interface. The single-stranded MB-P could thus tend to form a hairpin structure through the hybridization of the complementary sequences at both its ends. Such conformational changes result in the oxidation peak current of Fc decreases and that of MB increases, and the changes of dual signals are linear with the concentration of ATP. When "ΔI = ΔI(MB) + |ΔI(Fc)|" (ΔI(MB) and ΔI(Fc) are the change values of the oxidation peak currents of MB and Fc, respectively.) is used as the response signal for quantitative determination of ATP, the detection limit (1.9 nM) is much lower than that by using either MB-P or Fc-P alone. This new dual-signaling aptasensor is readily regenerated and shows good response toward the target. It will have important applications in the sensitive and selective electrochemical determination of other small molecules and proteins.