Fluorescent ferritin nanoparticles and application to the aptamer sensor

Vertasile ferritin nanocages: Applications in detection and bioimaging

Food safety and human health remain significant concerns in the food industry. Detecting food contaminants and diagnosing diseases are critical aspects. Ferritin, an iron storage protein widely found in nature, offers unique advantages. Its hollow protein nanocage structure, distinct interfaces, hydrophobic or hydrophilic channels, and B-C loop regions recognized by transferrin receptor 1 make ferritin versatile for detecting heavy metals, free radicals, and bioimaging both in vitro and in vivo. This review summarizes ferritin's general characteristics, its specific properties as biosensors, and its applications in food safety and in vivo imaging. It emphasizes not only ferritin's role in detecting heavy metals like mercury and chemical hazards but also its potential in early diagnosing chronic diseases such as tumors, macrophages, and kidney diseases. Further research into ferritin promises advancements in enhancing food safety and improving human health diagnostics.

Engineered human H-chain ferritin with reversed charge of the internal cavity exhibits RNA-mediated spongelike effect for loading RNA/DNA-binding molecules

Ferritins are globular proteins with an internal cavity that enables the encapsulation of a plethora of low-mass compounds. Unfortunately, the overall negative surface charge of ferritin's internal cavity hampers efficient loading of negatively charged molecules. Therefore, we produced a genetically engineered human H-chain ferritin containing a cationic RKRK domain, reversing the natural net charge of the cavity to positive, thus allowing for efficient encapsulation of negatively charged siRNA. Due to the reversed, positive charge mediated by RKRK domains, the recombinant ferritin produced in E. coli inherently carries a load of bacterial RNA inside its cavity, turning the protein into an effective sponge possessing high affinity for DNA/RNA-binding substances that can be loaded with markedly higher efficiency compared to the wildtype protein. Using doxorubicin as payload, we show that due to its loading through the RNA sponge, doxorubicin is released in a sustained manner, with a cytotoxicity profile similar to the free drug. In summary, this is the first report demonstrating a ferritin/nucleic acid hybrid delivery vehicle with a broad spectrum of properties exploitable in various fields of biomedical applications.

Protein nanoparticles directed cancer imaging and therapy

Cancer has been a serious threat to human health. Among drug delivery carriers, protein nanoparticles are unique because of their mild and environmentally friendly preparation methods. They also inherit desired characteristics from natural proteins, such as biocompatibility and biodegradability. Therefore, they have solved some problems inherent to inorganic nanocarriers such as poor biocompatibility. Also, the surface groups and cavity of protein nanoparticles allow for easy surface modification and drug loading. Besides, protein nanoparticles can be combined with inorganic nanoparticles or contrast agents to form multifunctional theranostic platforms. This review introduces representative protein nanoparticles applicable in cancer theranostics, including virus-like particles, albumin nanoparticles, silk protein nanoparticles, and ferritin nanoparticles. It also describes the common methods for preparing them. It then critically analyzes the use of a variety of protein nanoparticles in improved cancer imaging and therapy.

Multistage targeting and dual inhibiting strategies based on bioengineered tumor matrix microenvironment‐mediated protein nanocages for enhancing cancer biotherapy

Regulation of the apoptotic pathway plays a critical role in inducing tumor cell death and circumventing drug resistance. Survivin protein is the strongest inhibitor of apoptosis found so far. It is highly expressed in several cancers and is a promising target for cancer therapy. However, clinical applications are limited by incomplete inhibition of survivin expression. Here, we present a novel strategy that extended the release of YM155 (an effective survivin inhibitor that works by inhibiting the activity of survivin promoter) and TATm‐survivin (T34A) (TmSm) protein (survivin protein mutant with penetrating peptide, a potential anticancer protein therapeutic) via tumor matrix microenvironment‐mediated ferritin heavy chain nanocages (FTH1 NCs), enabling significant inhibition of survivin activity at both transcript and protein levels. FTS (FTH1‐matrix metalloproteinase‐2‐TmSm)/YM155 NC synthesis was easily scaled up, and these NCs could sequentially release TmSm protein through matrix metalloproteinase‐2 and promote YM155 to enter the nucleus via transferrin receptor 1 (TfR1) binding, which increased the cytotoxicity and apoptosis of Capan‐2 and A549 cells compared to that with individual drugs. Moreover, FTS/YM155 NCs enhanced drug accumulation at tumor sites and had a higher tumor inhibition rate (88.86%) than the compounds alone in A549 tumor‐bearing mice. In addition, FTS/YM155 NCs exerted significant survivin downregulation (4.43‐fold) and caspase‐3 upregulation (4.31‐fold) and showed better therapeutic outcomes without inducing organ injury, which highlights their promising future clinical application in precision therapy. This tumor microenvironment‐responsive platform could be harnessed to develop an effective therapy via multilevel inhibition of cancer targets.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Advancements of nature nanocage protein: preparation, identification and multiple applications of ferritins

Ferritin is an important iron storage protein, which is widely existed in all forms of life. Ferritin can regulate iron homeostasis when iron ions are lacking or enriched in the body, so as to avoid iron deficiency diseases and iron poisoning. Ferritin presents a hollow nanocage, which can store ions or other small molecular substances in the cavity. Therefore, ferritin shows its potential as a functional nanomaterial that can deliver nutrients or drugs in a targeted manner to improve bioavailability. Due to the special structure, the research on ferritin has attracted more and more attention in recent years. In this paper, the structural characteristics of ferritin were introduced, and the natural purification and prokaryotic expression methods of ferritin from different sources were described. At the same time, ferritin can bind to small molecules, so that it has the activity of small molecules, to construct a new type of ferritin. As a result, ferritin plays an important role as a nutrient substance, in targeted transport, and disease monitoring, etc. In conclusion, the yield of ferritin can be improved by means of molecular biology. Meanwhile, molecular modification can be used to make ferritin have unique activity and function, which lays a foundation for subsequent research. HighlightsThe molecular and structural properties of ferritins were clearly described.Isolation and purification technologies of ferritin were compared.Characterization, functions and molecular modifications mechanism of ferritin were reviewed.The applications of ferritin in pharmaceutical and food industry were prospected.

Fluorogenic Aptasensors with Small Molecules

Aptamers are single-stranded DNA or RNA molecules that can be identified through an iterative in vitro selection–amplification process. Among them, fluorogenic aptamers in response to small molecules have been of great interest in biosensing and bioimaging due to their rapid fluorescence turn-on signals with high target specificity and low background noise. In this review, we report recent advances in fluorogenic aptasensors and their applications to in vitro diagnosis and cellular imaging. These aptasensors modulated by small molecules have been implemented in different modalities that include duplex or molecular beacon-type aptasensors, aptazymes, and fluorogen-activating aptamer reporters. We highlight the working principles, target molecules, modifications, and performance characteristics of fluorogenic aptasensors, and discuss their potential roles in the field of biosensor and bioimaging with future directions and challenges.

Peptide-Mediated Immobilization on Magnetoferritin for Enzyme Recycling

Ferritin possess favorable properties because its exterior and interior surface can be applied to generate functional nanomaterials, which make them possible for enzyme immobilization and recycling. Here, we report the noncovalent immobilization of a genetically modified β-glucosidase onto the outer surface of synthetic magnetoferritin through the electrostatic interaction of a heterodimeric coiled-coil protein formed by coils containing lysine residues (K-coils) and coils containing glutamic acid (E-coils). The immobilized enzyme was characterized, and its enzymatic properties were evaluated. Furthermore, reusability of immobilized enzyme was demonstrated in aqueous solution under an applied magnetic field. The results showed that magnetoferritin was successfully prepared and it was an excellent support for enzyme immobilization. After three times usages, the retention rates were 93.75%, 82.5%, and 56.25%, respectively, demonstrating that immobilized enzyme possessed good retention efficiency and could be used as potential carrier for other biomolecules. The strategy of enzyme immobilization developed in this work can be applied, in general, to many other target molecules.

Re-designing ferritin nanocages for mercuric ion detection

Protein nanocages have recently received considerable attention in the fields of nanoscience and nanomedicine and have been used as either biotemplates for the preparation of a variety of nanomaterials or vehicles for drugs or imaging agents. However, their utilization for detection of heavy metal ions has yet to be explored. In this study, by grafting a mercury binding peptide (MBP) on the exterior surface of a recombinant human H-chain ferritin (rHuHF) nanocage, we successfully prepared a new protein nanocage (HuHF-MBP) which exhibits high binding capacity and affinity for Hg2+. The fluorescence of HuHF-MBP labeled with a green fluorescent dye fluorescein isothiocyanate (FITC) can be quenched by graphene oxide (GO), while addition of Hg2+ to the above solution recovered the quenched fluorescence in a dose-dependent manner. Thus, this system consisting of FITC-labeled HuHF-MBP and GO, where FITC and graphene oxide were used as fluorescent reporter probes, has great potential to be explored as a sensor for Hg2+ detection. Indeed, this newly constructed protein sensor exhibited high sensitivity and selectivity for Hg2+, and the limit of detection was 1.0 nM. The construction of this system provides an alternative strategy for the preparation of heavy metal ion sensors by using protein nanocages as biotemplates.

Ferritin-based anticancer metallodrug delivery: Crystallographic, analytical and cytotoxicity studies

The encapsulation of anticancer metal-based drugs within a protein nanocage represents a valuable strategy to improve the efficacy and selectivity of these compounds towards cancer cells. The preparation, characterization of the in vitro cytotoxicity and X-ray structures of several ferritin-metallodrug nanocomposites (mainly containing platinum-, ruthenium- and gold-based anticancer agents) are here reviewed. The molecular mechanisms of action of these Ft-metallodrug adducts are discussed and future directions in the field are outlined.

Aptamer based nanobiosensors: Promising healthcare devices

Nanobiosensors based on aptamer are extensively being studied as potent analytical tools in clinical analysis. These biosensors provide high sensitivity, fast response, specificity and desired portability in addition to simplicity and decreased cost compared to conventional methods. The purpose of this manuscript is to provide readers with an overview of current advances about electrochemical, electrochemiluminescent and photoelectrochemical aptasensors from the sea of available literature. These are mainly used for determination of protein-based biomarkers, especially for cancer diagnosis. Here in we have given special emphasis on nanosize-based aptasensors which have been reported to show considerable improvement in the analytical performance.

Optical and Electrochemical Aptasensors for Sensitive Detection of Streptomycin in Blood Serum and Milk

Detection and quantitation of antibiotic residues in blood serum and foodstuffs are in great demand. We have developed aptasensors for detection of streptomycin using electrochemical and optical methods. In the first method, an electrochemical aptasensor was developed for sensitive and selective detection of streptomycin, based on combination of exonuclease I (Exo I), complementary strand of aptamer (CS), arch shaped structure of aptamer (Apt)-CS conjugate, and gold electrode. The designed electrochemical aptasensor exhibited high selectivity toward streptomycin with a limit of detection (LOD) as low as 11.4 nM. Moreover, the developed electrochemical aptasensor was successfully used to detect streptomycin in milk and serum with LODs of 14.1 and 15.3 nM, respectively. In the second method, fluorescence quenching and colorimetric aptasensors were designed for detection of streptomycin based on aqueous gold nanoparticles (AuNPs) and double-stranded DNA (dsDNA). In the absence of streptomycin, aptamer/FAM-labeled complementary strand dsDNA is stable, resulting in the aggregation of AuNPs by salt bridge and an obvious color change from red to blue and strong emission of fluorescence. The colorimetric and fluorescence quenching aptasensors showed excellent selectivity toward streptomycin with limit of detections as low as 73.1 and 47.6 nM, respectively. The presented aptasensors were successfully used to detect streptomycin in milk and serum. For serum, LODs were determined to be 58.2 and 102.4 nM for fluorescence quenching and colorimetric aptasensors, respectively. For milk, LODs were calculated to be 56.2 and 108.7 nM for fluorescence quenching and colorimetric aptasensors, respectively.

Ferritin-EGFP Chimera as an Endogenous Dual-Reporter for Both Fluorescence and Magnetic Resonance Imaging in Human Glioma U251 Cells

A unique hybrid protein ferritin–enhanced green fluorescent protein (EGFP) was built to serve as an endogenous dual reporter for both fluorescence and magnetic resonance imaging (MRI). It consists of a human ferritin heavy chain (an iron-storage protein) at the N terminus, a flexible polypeptide in the middle as a linker, and an EGFP at the C terminus. Through antibiotic screening, we established stable human glioma U251 cell strains that expressed ferritin–EGFP under the control of tetracycline. These cells emitted bright green fluorescence and were easily detected by a fluorescent microscope. Ferritin–EGFP overexpression proved effective in triggering obvious intracellular iron accumulation as shown by Prussian blue staining and by MRI. Further, we found that ferritin–EGFP overexpression did not cause proliferation differences between experimental and control group cells when ferritin–EGFP was expressed for <96 hours. Application of this novel ferritin–EGFP chimera has a promising future for combined optical and MRI approaches to study in vivo imaging at a cellular level.

Fluorescent carbon nanoparticle-based lateral flow biosensor for ultrasensitive detection of DNA

We report a fluorescent carbon nanoparticle (FCN)-based lateral flow biosensor for ultrasensitive detection of DNA. Fluorescent carbon nanoparticle with a diameter of around 15nm was used as a tag to label a detection DNA probe, which was complementary with the part of target DNA. A capture DNA probe was immobilized on the test zone of the lateral flow biosensor. Sandwich-type hybridization reactions among the FCN-labeled DNA probe, target DNA and capture DNA probe were performed on the lateral flow biosensor. In the presence of target DNA, FCNs were captured on the test zone of the biosensor and the fluorescent intensity of the captured FCNs was measured with a portable fluorescent reader. After systematic optimizations of experimental parameters (the components of running buffers, the concentration of detection DNA probe used in the preparation of FCN-DNA conjugates, the amount of FCN-DNA dispensed on the conjugate pad and the dispensing cycles of the capture DNA probes on the test-zone), the biosensor could detect a minimum concentration of 0.4 fM DNA. This study provides a rapid and low-cost approach for DNA detection with high sensitivity, showing great promise for clinical application and biomedical diagnosis.

Genetic Assembly of Double-Layered Fluorescent Protein Nanoparticles for Cancer Targeting and Imaging

Hepatitis B virus capsid (HBVC), a self-assembled protein nanoparticle comprised of 180 or 240 subunit proteins, is used as a cage for genetic encapsulation of fluorescent proteins (FPs). The self-quenching of FPs is controlled by varying the spacing between FPs within the capsid structure. Double-layered FP nanoparticle possessing cancer cell-targeting capabilities is also produced by additionally attaching FPs and cancer cell receptor-binding peptides (affibodies) to the outer surface of the capsid. The generically modified HBVC with double layers of mCardinal FPs and affibodies (mC-DL-HBVC) exhibit a high fluorescence intensity and a strong photostability, and is efficiently internalized by cancer cells and significantly stable against intracellular degradation. The mC-DL-HBVC effectively detects tumor in live mice with enhanced tumor targeting and imaging efficiency with far less accumulation in the liver, compared to a conventional fluorescent dye, Cy5.5. This suggests the great potential of mC-DL-HBVC as a promising contrast agent for in vivo tumor fluorescence imaging.

Defining the copper binding aptamotif and aptamer integrated recovery platform (AIRP)

The potential copper binding sites in aptamers have been predicted on the basis of secondary structures and the binding affinity of aptamers with copper. Out of the 4 aptamers (Cu-A1 to Cu-A4) selected by SELEX and examined in the present study, the Cu-A2 aptamer shows the highest binding affinity to copper with the lowest K_D value of 1.83 × 10^-11 M. In order to confirm the binding of copper to the proposed region, the binding affinity was experimentally validated using mutation and deletion analysis. We have confirmed that the high G-C pairing patterns and short stem-interval distance play important roles in copper binding. Aptamer specificity was also verified against diverse heavy metals. We also demonstrate an Aptamer Integrated Recovery Platform (AIRP) to recover copper from acidic mine drainage. AIRP can be easily regenerated at least 20 times without significant deterioration of the retrieval performance. To the best of our knowledge, AIRP is the first demonstration of copper specific recovery using aptamers. This can be scaled up and would have diverse applications in metal contaminated water treatment, recovery and as a potential biosensor for environmental analysis, monitoring, and risk assessment.

Catalytic Macroporous Biohydrogels Made of Ferritin-Encapsulated Gold Nanoparticles

Reported is a modular approach for the incorporation and stabilization of gold nanoparticles inside a three-dimensional macroporous hydrogel made of ferritin. The strategy, which involves the dynamic templating of surfactant H₁ domains, demineralization, and remineralization helps to overcome aggregation and degradation issues usually associated with bare-metal-based nanocatalysts. The catalytic activity of the so-synthesized bionanocomposite hydrogel was demonstrated in both nitroaldol (Henry) and nitroreduction model reactions in aqueous solution at room temperature. An interesting synergistic effect between basic residues of the protein and the gold nanoparticles was found in the nitroaldol reaction when carried out in water in the presence of a phase-transfer catalyst. Furthermore, the reduction of 4-nitrophenol and 4-nitroaniline catalyzed by the nanocomposite scaffold in the presence of NaBH₄ proceeded significantly faster than that using other known Au- and Ag-based catalysts under similar conditions.

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.

Enhanced electrogenerated chemiluminescence behavior of C3N4 QDs@ C3N4 nanosheet and its signal-on aptasensing for platelet derived growth factor

A novel g-C₃N₄ nanosheets embedded with C₃N₄ QDs nanocomposites (QD@CNNS) was prepared by simple oxidation using hydrogen peroxide and UV light irradiation. This nanocomposite exhibits more stable and stronger electrochemiluminescent (ECL) behavior compared with CNNS. Coupling this nanocomposite with Fc-labeled aptamer, a signal-on aptasensor for platelet derived growth factor BB (PDGF-BB) is fabricated. Initially, the Fc-labeled aptamer binds onto QD@CNNS via π-π conjugation and electrostatic interaction, quenching ECL emission from QD@CNNS. The introduction of target efficiently recovers the ECL signal by the formation of PDGF-BB/aptamer complex. The ECL intensity is proportion to the concentration of PDGF-BB in the range of 0.02-80nM with a detection limit of 0.013nM. This work demonstrates a simple synthesis method to obtain QD@CNNS with excellent ECL behavior, and opens up the application of g-C₃N₄ nanocomposite in signal-on aptasensing.

Engineered Human Ferritin Nanoparticles for Direct Delivery of Tumor Antigens to Lymph Node and Cancer Immunotherapy

Efficient delivery of tumor-specific antigens (TSAs) to lymph nodes (LNs) is essential to eliciting robust immune response for cancer immunotherapy but still remains unsolved. Herein, we evaluated the direct LN-targeting performance of four different protein nanoparticles with different size, shape, and origin [Escherichia coli DNA binding protein (DPS), Thermoplasma acidophilum proteasome (PTS), hepatitis B virus capsid (HBVC), and human ferritin heavy chain (hFTN)] in live mice, using an optical fluorescence imaging system. Based on the imaging results, hFTN that shows rapid LN targeting and prolonged retention in LNs was chosen as a carrier of the model TSA [red fluorescence protein (RFP)], and the flexible surface architecture of hFTN was engineered to densely present RFPs on the hFTN surface through genetic modification of subunit protein of hFTN. The RFP-modified hFTN rapidly targeted LNs, sufficiently exposed RFPs to LN immune cells during prolonged period of retention in LNs, induced strong RFP-specific cytotoxic CD8⁺ T cell response, and notably inhibited RFP-expressing melanoma tumor growth in live mice. This suggests that the strategy using protein nanoparticles as both TSA-carrying scaffold and anti-cancer vaccine holds promise for clinically effective immunotherapy of cancer.

Engineering protein interfaces yields ferritin disassembly and reassembly under benign experimental conditions

Ferritin nanocages are promising platforms for drug encapsulation. However, extreme conditions (pH ≤ 2) required for dissociation limit their application. Here, we engineered protein interfaces to yield ferritin nanocages which disassemble at pH 4.0 and reassemble at pH 7.5. During this process, bioactive molecules can be encapsulated within the protein cavity.

Nanoparticles and DNA - a powerful and growing functional combination in bionanotechnology

Functionally integrating DNA and other nucleic acids with nanoparticles in all their different physicochemical forms has produced a rich variety of composite nanomaterials which, in many cases, display unique or augmented properties due to the synergistic activity of both components. These capabilities, in turn, are attracting greater attention from various research communities in search of new nanoscale tools for diverse applications that include (bio)sensing, labeling, targeted imaging, cellular delivery, diagnostics, therapeutics, theranostics, bioelectronics, and biocomputing to name just a few amongst many others. Here, we review this vibrant and growing research area from the perspective of the materials themselves and their unique capabilities. Inorganic nanocrystals such as quantum dots or those made from gold or other (noble) metals along with metal oxides and carbon allotropes are desired as participants in these hybrid materials since they can provide distinctive optical, physical, magnetic, and electrochemical properties. Beyond this, synthetic polymer-based and proteinaceous or viral nanoparticulate materials are also useful in the same role since they can provide a predefined and biocompatible cargo-carrying and targeting capability. The DNA component typically provides sequence-based addressability for probes along with, more recently, unique architectural properties that directly originate from the burgeoning structural DNA field. Additionally, DNA aptamers can also provide specific recognition capabilities against many diverse non-nucleic acid targets across a range of size scales from ions to full protein and cells. In addition to appending DNA to inorganic or polymeric nanoparticles, purely DNA-based nanoparticles have recently surfaced as an excellent assembly platform and have started finding application in areas like sensing, imaging and immunotherapy. We focus on selected and representative nanoparticle-DNA materials and highlight their myriad applications using examples from the literature. Overall, it is clear that this unique functional combination of nanomaterials has far more to offer than what we have seen to date and as new capabilities for each of these materials are developed, so, too, will new applications emerge.

Reversible and multi-cyclic protein-protein interaction in bacterial cellulosome-mimic system using rod-shaped viral nanostructure

The type II cohesin domain and type II dockerin of bacterial cellulosome were cloned from Clostridium thermocellum and expressed with the fusion of tobacco mosaic virus coat protein (TMVcp) and enhanced green fluorescent protein (EGFP), respectively, in Escherichia coli. The TMVcp-cohesin fusion protein was assembled to the stable and rod-shaped nanostructure (TMVcp-Coh rod) under a particular buffer condition, where many active cohesin proteins are biologically and densely displayed around the 3-dimensional surface of TMVcp-Coh rod. Using EGFP-dockerin as a fluorescent reporter, we confirmed that the Ca(2+)-dependent binding and dissociation between native cohesin and dockerin were reproduced with the two recombinant fusion proteins, TMVcp-cohesin and EGFP-dockerin. The multi-cyclic binding-dissociation operation of TMVcp-Coh rod and EGFP-dockerin was successfully performed with maintaining the reversible cohesin-dockerin interaction in every cycle. EGFP that was fused to dockerin as a proof-of-concept here can be switched to other functional proteins/peptides that need to be used in multi-cyclic operation.

Vascular Accessibility of Endothelial Targeted Ferritin Nanoparticles

Targeting nanocarriers to the endothelium, using affinity ligands to cell adhesion molecules such as ICAM-1 and PECAM-1, holds promise to improve the pharmacotherapy of many disease conditions. This approach capitalizes on the observation that antibody-targeted carriers of 100 nm and above accumulate in the pulmonary vasculature more effectively than free antibodies. Targeting of prospective nanocarriers in the 10-50 nm range, however, has not been studied. To address this intriguing issue, we conjugated monoclonal antibodies (Ab) to ICAM-1 and PECAM-1 or their single chain antigen-binding fragments (scFv) to ferritin nanoparticles (FNPs, size 12 nm), thereby producing Ab/FNPs and scFv/FNPs. Targeted FNPs retained their typical symmetric core-shell structure with sizes of 20-25 nm and ∼4-5 Ab (or ∼7-9 scFv) per particle. Ab/FNPs and scFv/FNPs, but not control IgG/FNPs, bound specifically to cells expressing target molecules and accumulated in the lungs after intravenous injection, with pulmonary targeting an order of magnitude higher than free Ab. Most intriguing, the targeting of Ab/FNPs to ICAM-1, but not PECAM-1, surpassed that of larger Ab/carriers targeted by the same ligand. These results indicate that (i) FNPs may provide a platform for targeting endothelial adhesion molecules with carriers in the 20 nm size range, which has not been previously reported; and (ii) ICAM-1 and PECAM-1 (known to localize in different domains of endothelial plasmalemma) differ in their accessibility to circulating objects of this size, common for blood components and nanocarriers.

Self-Assembly of Ferritin Nanoparticles into an Enzyme Nanocomposite with Tunable Size for Ultrasensitive Immunoassay

The self-assembly of nanoparticles into larger superstructures is a powerful strategy to develop novel functional nanomaterials, as these superstructures display collective properties that are different to those displayed by individual nanoparticles or bulk samples. However, there are increasing bottlenecks in terms of size control and multifunctionalization of nanoparticle assemblies. In this study, we developed a self-assembly strategy for construction of multifunctional nanoparticle assemblies of tunable size, through rational regulation of the number of self-assembling interaction sites on each nanoparticle. As proof-of-principle, a size-controlled enzyme nanocomposite (ENC) was constructed by self-assembly of streptavidin-labeled horseradish peroxidase (SA-HRP) and autobiotinylated ferritin nanoparticles (bFNP). Our ENC integrates a large number of enzyme molecules, together with a streptavidin-coated surface, allowing for a drastic increase in enzymatic signal when the SA is bound to a biotinylated target molecule. As result, a 10 000-fold increase in sensitivity over conventional enzyme-linked immunosorbent assays (ELISA) methods was achieved in a cardiac troponin immunoassay. Our method presented here should provide a feasible approach for constructing elaborate multifunctional superstructures of tunable size useful for a broad range of biomedical applications.

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.

Colorimetric and fluorescence quenching aptasensors for detection of streptomycin in blood serum and milk based on double-stranded DNA and gold nanoparticles

Antibiotic residues in animal foodstuffs are of great concern to consumers. In this study, fluorescence quenching and colorimetric aptasensors were designed for detection of streptomycin based on aqueous gold nanoparticles (AuNPs) and double-stranded DNA (dsDNA). In the absence of streptomycin, aptamer/FAM-labeled complementary strand dsDNA is stable, resulting in the aggregation of AuNPs by salt and an obvious color change from red to blue and strong emission of fluorescence. In the presence of streptomycin, aptamer binds to its target and FAM-labeled complementary strand adsorbs on the surface of AuNPs. So the well-dispersed AuNPs remain stable against salt-induced aggregation with a wine-red color and the fluorescence of FAM-labeled complimentary strand is efficiently quenched by AuNPs. The colorimetric and fluorescence quenching aptasensors showed excellent selectivity toward streptomycin with limit of detections as low as 73.1 and 47.6 nM, respectively. The presented aptasensors were successfully used to detect streptomycin in milk and serum.

Enzyme-free and label-free fluorescence aptasensing strategy for highly sensitive detection of protein based on target-triggered hybridization chain reaction amplification

Proteins are of great importance in medical and biological fields. In this paper, a novel fluorescent aptasensing strategy for protein assay has been developed based on target-triggered hybridization chain reaction (HCR) and graphene oxide (GO)-based selective fluorescence quenching. Three DNA probes, a helper DNA probe (HP), hairpin probe 1 (H1) and hairpin probe 2 (H2) are ingeniously designed. In the presence of the target, the aptamer sequences in HP recognize the target to form a target-aptamer complex, which causes the HP conformation change, and then triggers the chain-like assembly of H1 and H2 through the hybridization chain reaction, generating a long chain of HP leading complex of H1 and H2. At last the fluorescence indicator SYBR Green I (SG) binds with the long double strands of the HCR product through both intercalation and minor groove binding. When GO was added into the solutions after HCR, the free H1, H2 and SG would be closely adsorbed onto GO surface via π-π stacking. However, the HCR product cannot be adsorbed on GO surface, thereby the SG bound to HCR product gives a strong fluorescence signal dependent on the concentration of the target. With the use of platelet-derived growth factor BB (PDGF-BB) as the model analyte, this newly designed protocol provides a highly sensitive fluorescence detection of PDGF-BB with a limit of detection down to 1.25 pM, and also exhibit good selectivity and applicability in complex matrixes. Therefore, the proposed aptasensing strategy based on target-triggered hybridization chain reaction amplification should have wide applications in the diagnosis of genetic diseases due to its simplicity, low cost, and high sensitivity at extremely low target concentrations.

Ultrasensitive detection of lead (II) based on fluorescent aptamer-functionalized carbon nanotubes

Lead contamination is a serious environmental problem with toxic effects in human. Here, we developed a simple and sensitive sensing method employing ATTO 647N/aptamer-SWNT ensemble for detection of Pb(2+). This method is based on the super quenching capability of single-walled carbon nanotubes (SWNTs), high affinity of the aptamer toward Pb(2+) and different propensities of ATTO 647N-aptamer and ATTO 647N-aptamer/Pb(2+) complex for adsorption on SWNTs. In the absence of Pb(2+), the fluorescence of ATTO 647N-aptamer is efficiently quenched by SWNTs. Upon addition of Pb(2+), the aptamer binds to its target, leading to the formation of a G-quadruplex/Pb(2+) complex and does not interact with SWNTs and ATTO 647N-aptamer starts fluorescing. This sensor exhibited a high selectivity toward Pb(2+) and a limit of detection (LOD) as low as 0.42 nM was obtained. Also this sensor could be applied for detection of Pb(2+) ions in tap water and biological sample like serum with high sensitivity.

Tuberculosis diagnosis using immunodominant, secreted antigens of Mycobacterium tuberculosis

Tuberculosis (TB) remains a major public health concern in most low-income countries. Hence, rapid and sensitive TB diagnostics play an important role in detecting and preventing the disease. In addition to established diagnostic methods, several new approaches have been reported. Some techniques are simple but time-consuming, while others require complex instrumentation. One prominent and readily available approach is to detect proteins that Mycobacterium tuberculosis secretes, such as Mpt64, the 6-kDa early secreted antigenic target (Esat6), the 10-kDa culture filtrate protein (Cfp10), and the antigen 85 (Ag85) complex. Although their functions are not fully understood, a growing body of molecular evidence implicates them in M. tuberculosis virulence. Currently these biomarkers are either being used or investigated for use in skin patch tests, biosensor analyses, and immunochromatographic, immunohistochemical, polymerase chain reaction-based, and enzyme-linked immunosorbent assays. This review provides a comprehensive discussion of the roles these immunodominant antigens play in M. tuberculosis pathogenesis and compares diagnostic methods based on the detection of these proteins with more established tests for TB.

Aptamer-modified nanoparticles as biosensors

Aptamers are short oligonucleotides that are capable of selectively binding to their corresponding target. Therefore, they can be thought of as a nucleic acid-based alternative to antibodies and can substitute for their amino acid-based counterparts in analytical applications, including as receptors in biosensors. Here they offer several advantages because their nucleic acid nature and their binding via an induced fit mechanism enable novel sensing strategies. In this article, the utilization of aptamers as novel bio-receptors in combination with nanoparticles as transducer elements is reviewed. In addition to these analytical applications, the medical relevance of aptamer-modified nanoparticles is described.

Colorimetric and ultrasensitive bioassay based on a dual-amplification system using aptamer and DNAzyme

Rapid detection of ultralow amount of biomarkers in a biologically complex mixture remains a major challenge. Herein, we report a novel aptamer-based protein detection assay that integrates two signal amplification processes, namely, polymerase-mediated rolling-circle amplification (RCA) and DNA enzyme-catalyzed colorimetric reaction. The target biomarker is captured in a sandwich assay by primary aptamer-functionalized microbeads (MBs) and a secondary aptamer that is connected to a RCA primer/circular template complex. RCA reaction, which amplifies the single biomarker binding events by a factor of hundreds to thousands (the first amplification) produces a long DNA molecule containing multiple DNAzyme units. The peroxidase-like DNAzyme catalyzes the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (the second amplification), which generates a blue-green colorimetric signal. This new biosensing platform permits the ultrasensitive, label-free, colorimetric detection of biomarker in real time. Using platelet-derived growth factor B-chain (PDGF-BB) as a model system, we demonstrated that our assay can detect a protein marker specifically in a serum-containing medium, at a concentration as low as 0.2 pg/mL in ∼2 h, which rivals traditional assays such as ELISA. We anticipate this simple methodology for biomarker detection can find utility in point-of-care applications.

Aptamer-based fluorescent biosensors

Selected from random pools of DNA or RNA molecules through systematic evolution of ligands by exponential enrichment (SELEX), aptamers can bind to target molecules with high affinity and specificity, which makes them ideal recognition elements in the development of biosensors. To date, aptamer-based biosensors have used a wide variety of detection techniques, which are briefly summarized in this article. The focus of this review is on the development of aptamer-based fluorescent biosensors, with emphasis on their design as well as properties such as sensitivity and specificity. These biosensors can be broadly divided into two categories: those using fluorescently-labeled aptamers and others that employ label-free aptamers. Within each category, they can be further divided into "signal-on" and "signal-off" sensors. A number of these aptamer-based fluorescent biosensors have shown promising results in biological samples such as urine and serum, suggesting their potential applications in biomedical research and disease diagnostics.

Multifunctional ferritin cage nanostructures for fluorescence and MR imaging of tumor cells

Bionanoparticles and nanostructures have attracted increasing interest as versatile and promising tools in many applications including biosensing and bioimaging. In this study, to image and detect tumor cells, ferritin cage-based multifunctional hybrid nanostructures were constructed that: (i) displayed both the green fluorescent protein and an Arg-Gly-Asp peptide on the exterior surface of the ferritin cages; and (ii) incorporated ferrimagnetic iron oxide nanoparticles into the ferritin interior cavity. The overall architecture of ferritin cages did not change after being integrated with fusion proteins and ferrimagnetic iron oxide nanoparticles. These multifunctional nanostructures were successfully used as a fluorescent imaging probe and an MRI contrast agent for specifically probing and imaging α(v)β(3) integrin upregulated tumor cells. The work provides a promising strategy for tumor cell detection by simultaneous fluorescence and MR imaging.