Increased sensitivity in antigen detection with fluorescent latex nanosphere-IgG antibody conjugates

Strategies Employed to Design Biocompatible Metal Nanoparticles for Medical Science and Biotechnology Applications

The applicability of nanomaterials has evolved in biomedical domains thanks to advances in biocompatibility strategies and the mitigation of cytotoxic effects, allowing diagnostics, imaging, and therapeutic approaches. The application of nanoparticles (NP), particularly metal nanoparticles (mNPs), such as gold (Au) and silver (Ag), includes inherent challenges related to the material characteristics, surface modification, and bioconjugation techniques. By tailoring the surface properties through appropriate coating with biocompatible molecules or functionalization with active biomolecules, researchers can reach a harmonious interaction with biological systems or samples (mostly fluids or tissues). Thus, this review highlights the mechanisms associated with the obtention of biocompatible mNP and presents a comprehensive overview of methods that facilitate safe and efficient production. Therefore, we consider this review to be a valuable resource for all researchers navigating this dynamic field.

γ-Functional Iminiumthiolactones for the Single and Double Modification of Peptides

Thiolactones (TL) can be readily incorporated into polymeric materials and have been extensively used as a ligation strategy despite their limited reactivity toward amine-containing substrates. Comparatively, iminiumthiolactones (ITL) are much more reactive, yet to this day, only the nonsubstituted ITL known as Traut's reagent is commercially available and used. In this work, we advance current TL/ITL chemistry by introducing reactive side groups to the ITL heterocycle in the γ-position, which can be orthogonally modified without affecting the ITL heterocycle itself. To study the reactivity of γ-functional ITLs, we subject one of our derivatives (γ-allyl-functional ITL 3b) to model reactions with several peptides and a chosen protein (lysozyme C). Using mild reaction conditions, we successfully demonstrate that the γ-functional ITL exhibits orthogonal and enhanced reactivity in a single or double modification while introducing a new functional handle to the biological substrate. We believe that γ-functional ITLs will advance the original Traut chemistry and open promising opportunities for the bioconjugation of biological building blocks to existing functional molecules, polymers, and materials.

Peroxidase-Mimicking Activity of Biogenic Gold Nanoparticles Produced from Prunus nepalensis Fruit Extract: Characterizations and Application for the Detection of Mycobacterium bovis

In the present study, a facile, eco-friendly, and controlled synthesis of gold nanoparticles (Au NPs) using Prunus nepalensis fruit extract is reported. The biogenically synthesized Au NPs possess ultra-active intrinsic peroxidase-like activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Chemical analysis of the fruit extract demonstrated the presence of various bioactive molecules such as amino acids (l-alanine and aspartic acids), organic acids (benzoic acid and citric acid), sugars (arabinose and glucose), phenolic acid, and bioflavonoids (niacin and myo-inositol), which likely attributed to the formation of stable biogenic Au NPs with excellent peroxidase-mimicking activity. In comparison with the natural horseradish peroxidase (HRP) enzyme, the biogenic Au NPs displayed a 9.64 times higher activity with regard to the reaction velocity at 6% (v/v) H2O2, presenting a higher affinity toward the TMB substrate. The Michaelis-Menten constant (KM) values for the biogenic Au NPs and HRP were found to be 6.9 × 10-2 and 7.9 × 10-2 mM, respectively, at the same concentration of 100 pM. To investigate its applicability for biosensing, a monoclonal antibody specific for Mycobacterium bovis (QUBMA-Bov) was directly conjugated to the surface of the biogenic Au NPs. The obtained results indicate that the biogenic Au NPs-QUBMA-Bov conjugates are capable of detecting M. bovis based on a colorimetric immunosensing method within a lower range of 100 to 102 cfu mL-1 with limits of detection of ∼53 and ∼71 cfu mL-1 in an artificial buffer solution and in a soft cheese spiked sample, respectively. This strategy demonstrates decent specificity in comparison with those of other bacterial and mycobacterial species. Considering these findings together, this study indicates the potential for the development of a cost-effective biosensing platform with high sensitivity and specificity for the detection of M. bovis using antibody-conjugated Au nanozymes.

Catalytic ferromagnetic gold nanoparticle immunoassay for the detection and differentiation of Mycobacterium tuberculosis and Mycobacterium bovis

A ferromagnetic gold nanoparticle based immune detection assay, exploiting the enhanced signal amplification of inorganic nanozymes, was developed and evaluated for its potential application in the detection of Mycobacterium tuberculosis complex (MTBC) organisms, and simultaneous identification of Mycobacterium bovis. Ferromagnetic gold nanoparticles (Au-Fe₃O₄ NPs) were prepared and their intrinsic peroxidase-like activity exploited to catalyse 3,3',5',5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). When the Au-Fe₃O₄ NPs were functionalised by direct coupling with MTBC-selective antibodies, a nanoparticle based immune detection assay (NPIDA) was developed which could detect Mycobacterium tuberculosis (MTB) and differentiate M. bovis. In the assay, the intrinsic magnetic capability of the functionalised Au-Fe₃O₄ NPs was used in sample preparation to capture target bacterial cells. These were incorporated into a novel immunoassay which used species selective monoclonal antibodies (mAb) to detect bound target. The formation of a blue TMB oxidation product, with a peak absorbance of 370 nm, indicated successful capture and identification of the target. The detection limit of the NPIDA for both MTB and M. bovis was determined to be comparable to conventional ELISA using the same antibodies. Although limited matrix effects were observed in either assay, the NPIDA offers a reduced time to confirmatory identification. This novel NPIDA was capable of simultaneous sample concentration, purification, immunological detection and speciation. To our knowledge, it represents the first immune-based diagnostic test capable of identifying MTBC organisms and simultaneously differentiating M. bovis.

Detection of PD-L1 Expression in Temozolomide-Resistant Glioblastoma by Using PD-L1 Antibodies Conjugated with Lipid‑Coated Superparamagnetic Iron Oxide

Purpose

Targeted superparamagnetic iron oxide (SPIO) nanoparticles are a promising tool for molecular magnetic resonance imaging (MRI) diagnosis. Lipid-coated SPIO nanoparticles have a nonfouling property that can reduce nonspecific binding to off-target cells and prevent agglomeration, making them suitable contrast agents for molecular MRI diagnosis. PD-L1 is a poor prognostic factor for patients with glioblastoma. Most recurrent glioblastomas are temozolomide resistant. Diagnostic probes targeting PD-L1 could facilitate early diagnosis and be used to predict responses to targeted PD-L1 immunotherapy in patients with primary or recurrent glioblastoma. We conjugated lipid-coated SPIO nanoparticles with PD-L1 antibodies to identify PD-L1 expression in glioblastoma or temozolomide-resistant glioblastoma by using MRI.

Methods

The synthesized PD-L1 antibody-conjugated SPIO (PDL1-SPIO) nanoparticles were characterized using dynamic light scattering, zeta potential assays, transmission electron microscopy images, Prussian blue assay, in vitro cell affinity assay, and animal MRI analysis.

Results

PDL1-SPIO exhibited a specific binding capacity to PD-L1 of the mouse glioblastoma cell line (GL261). The presence and quantity of PDL1-SPIO in temozolomide-resistant glioblastoma cells and tumor tissue were confirmed through Prussian blue staining and in vivo T2* map MRI, respectively.

Conclusion

This is the first study to demonstrate that PDL1-SPIO can specifically target temozolomide-resistant glioblastoma with PD-L1 expression in the brain and can be quantified through MRI analysis, thus making it suitable for the diagnosis of PD-L1 expression in temozolomide-resistant glioblastoma in vivo.

Bimodal size distribution immuno-quantum dots for fluorescent western blotting assay with high sensitivity and extended dynamic range

A highly sensitive quantum dot (QD)-based western blot assay with extended dynamic range was developed. Bimodal size distribution QD (BQ) immunoprobes composed of small size single QD (7.3 nm) and big size QD nanobead (QB) (82.9 nm) were employed for fluorescent western blot immunoassay on a membrane. Small size QD immunoprobes contributed to wider dynamic range of assay, while big size QB immunoprobes provided higher detection sensitivity. This BQ-based western blot assay can achieve a wide dynamic range (from 7.8 to 4000 ng IgG) and is nearly as sensitive as commercial available ultrasensitive chemiluminescent methods, just using a simple gel imager with UV light (365 nm) excitation and red light filter (610 nm). The fluorescent signals of BQ western blot were stable for 10 min, while chemiluminescent signals faded after 1 min. Moreover, this BQ immunoprobe was utilized for the detection of housekeeping protein and specific target proteins in complex cell lysate samples. The limit of detection of housekeeping protein is 0.25 μg of cell lysate, and the signal intensities were proportional to loading protein amount in a wide range from 0.61 to 80 μg. We believe that this new strategy of bimodal size distribution nanoparticles can also be expanded for other functional nanoparticle-based biological assays to improve the sensitivity and extend the dynamic range. Graphical abstract.

Ratiometric Reactive Oxygen Species Nanoprobe for Noninvasive In Vivo Imaging of Subcutaneous Inflammation/Infection

Release of reactive oxygen species (ROS) accompanied with acute inflammation and infection often results in cell death and tissue injury. Several ROS-reactive bioluminescent probes have been investigated in recent years to detect ROS activity in vivo. Unfortunately, these probes cannot be used to quantify the degree of ROS activity and inflammatory responses due to the fact that the extent of the bioluminescent signals is also probe-concentration dependent. To address this challenge, we fabricated a ratiometric ROS probe in which both ROS-sensitive chemiluminescent agents and ROS-insensitive fluorescent reference dye were conjugated to particle carriers. The bioluminescence/reference fluorescence intensity ratios was calculated to reflect the extent of localized ROS activities while circumventing the variations in bioluminescent intensities associated with the ROS probe concentrations. The physical and chemical properties of the ratiometric probes were characterized. Furthermore, we assessed the accuracy and reproducibility of the probe in detecting ROS in vitro. The ability of the ratiometric probes to detect ROS production in inflamed/infected tissues was also examined using animal models of inflammation and infection. The overall results imply that ratiometric ROS probes can rapidly and non-invasively detect and quantify the extent of inflammatory responses and bacterial infection on wounds in real time.

Comparison of four methods for the biofunctionalization of gold nanorods by the introduction of sulfhydryl groups to antibodies

Introducing sulfhydryl groups to biomolecules to functionalize gold nanorods (GNRs) is an attractive method that involves the creation of a strong Au-S bond. Previously, we developed a facile method to functionalize GNR surfaces by thiolating antibodies using Traut's reagent. In the current study, we evaluated several methods for the introduction of thiol groups onto the surface of GNRs by using Traut's reagent, dithiotreitol (DTT), dithiolaromatic PEG6-CONHNH₂, and thiol-polyethylene glycolamine (SH-PEG-NH₂) combined with EDC reaction. We showed that the four above-mentioned thiolation methods can efficiently functionalize GNRs and simplify the functionalization procedures. The formed GNR-bioconjugates showed superior stability without compromising the biological activity. The GNR nanochip prepared with these four thiolated antibodies can detect human IgG targets with specificity. However, SH-PEG-NH₂ combined with EDC reaction may affect the amount of functionalized GNRs because of the efficiency of thiol moiety linkage to antibodies, thereby affecting the sensitivity of the GNR sensor. The introduction of a thiol group to antibodies by using Traut's reagent, DTT, and PEG6-CONHNH₂ allowed for direct immobilization onto the GNR surface, improved the efficacy of functionalized GNRs, and increased the sensitivity in response to target detection as a biosensor. Given that PEG6-CONHNH₂ modification requires glycosylated biomolecules, Traut's reagent and DTT thiolation are recommended as universal applications of GNR biofunctionalization and can be easily extended to other sensing applications based on other gold nanostructures or new biomolecules.

Gold nanorod biochip functionalization by antibody thiolation

Conjugation of biomolecules on gold nanorod (GNR) surfaces is the basis for successful applications in biosensing, imaging, and drug delivery. Current functionalization methods are often problematic, involving multi-step nanoparticle modification to replace surfactant bilayer, delicate nanoparticle protection during surfactant exchange, and material loss due to inevitable aggregation. Instead of intensive surface modification of GNRs, we describe herein a facile method to functionalize gold nanorod surfaces via covalent Au-S bonds by thiolating receptors. The resulting GNR-bioconjugates showed superior dispersion and stability in buffer for months without morphology change and aggregation. ELISA tests confirmed the high biofunctionality of the thiolated anti-IgG moieties immobilized on the GNR surfaces. Furthermore, this simple method facilitated a straightforward functionalization of GNR assembly on glass substrate to construct a specific biochip, which can detect human IgG targets in a label-free fashion with high sensitivity and specificity. Compared to electropolymeric coating to functionalize the GNR, our method exhibited a five-fold enhancement in the spectral sensitivity to refractive index change caused by the target binding. This universal GNR bioconjugation method can be extended to bind different proteins and antibodies for development of biosensors or drug delivery.

In vivo imaging of infection using a bacteria-targeting optical nanoprobe

Wound and device-associated infection is a leading cause for morbidity and mortality. As such, rapid and early diagnosis of bacterial colonization is critical to infection treatment. The current diagnostic methods however, are not able to meet this requirement. Therefore, there is a practical need for the development of a new method to rapidly identify colonized bacteria. This study aims to develop optical nanoprobes that can detect and quantify the number of colonized bacteria in real time. To this end, we have synthesized an imaging nanoprobe with three elements: Concanavalin A (Con A) as a bacterial targeting ligand, a nanoparticle carrier, and a near infrared fluorescent dye. An MTS assay revealed that the bacteria nanoprobe is cell compatible. In vitro testing further showed that the bacteria nanoprobe had a very high specificity and affinity to bacteria. Using a murine wound and catheter infection model, we found that the bacteria nanoprobes can rapidly detect and quantify the extent of bacterial colonization on wounds and catheters in real time.

An amino acid-based heterofunctional cross-linking reagent

We describe the synthesis and characterization of a new lysine-based heterofunctional cross-linking reagent. It carries two readily available aminooxy functionalities and an activated and protected thiol group that is capable of generating reducible disulfides, the former enable bioorthogonal modification of ketones and aldehydes by the formation of an oxime bond. The efficacy of the linker was proven by coupling two doxorubicin molecules to the functionalized amino acid core and the subsequent bioconjugation of this drug conjugate with a thiolated antibody.

Liposomes functionalized to overcome the blood-brain barrier and to target amyloid-β peptide: the chemical design affects the permeability across an in vitro model

Purpose

We investigated the ability of amyloid-β-targeting liposomes, decorated with an anti-transferrin receptor antibody, to cross the blood–brain barrier (BBB), comparing two antibody ligation techniques.

Methods

Fluorescent or radiolabeled liposomes composed of sphingomyelin/cholesterol and containing phosphatidic acid, known to bind amyloid-β, were further functionalized with the anti-transferrin receptor antibody RI7217. Two different techniques were used to attach RI7217 to the liposomes surface: biotin/streptavidin linkage or thiol–maleimide covalent ligation. Surface plasmon resonance (SPR) and immunoblotting were employed to assess the nanoparticles’ binding performances. Confocal microscopy and radiochemical techniques were used for uptake and permeability studies on an in vitro BBB model made of human brain capillary endothelial cells hCMEC/D3.

Results

Immunoblotting experiments showed that RI7217-functionalized liposomes bind to transferrin receptor independently of the procedure employed to ligate their surface with the antibody, while SPR experiments showed a slightly higher affinity for covalently functionalized nanoliposomes. The functionalization with RI7217 did not affect the liposomes’ affinity for amyloid-β. The functionalization of liposomes with RI7217, independently of the ligation procedure, gave higher values of uptake and permeability across the barrier model in comparison to the nondecorated ones, without cell monolayer alterations. Of note, the best performing particles were those covalently coupled with the antibody. The ratios of the two radiolabeled lipids (³H-sphingomyelin and ¹⁴C-phosphatidic acid) present in the liposome bilayer were found to be similar in the apical and in the basolateral compartments of the barrier model, suggesting that liposomes were transported intact across the cell monolayer. Confocal experiments showed no co-localization of RI7217-liposomes with early/late endosomes or early lysosomes.

Conclusion

Our results suggest that RI7217 promotes the in vitro barrier crossing of liposomes containing phosphatidic acid, targeting the Alzheimer’s disease amyloid-β peptide. Moreover, for the first time, we prove herein the superior efficiency of covalent coupling of RI7217 versus biotin/streptavidin ligation to facilitate liposomes in overcoming the BBB in vitro.

Methods for conjugating antibodies to nanocarriers

Antibodies are one of the most commonly used targeting ligands for nanocarriers, mainly because they are specific, have a strong binding affinity, and are available for a number of disease biomarkers. The bioconjugation chemistry can be a crucial factor in determining the targeting efficiency of drug delivery and should be chosen on a case-by-case basis. An antibody consists of a number of functional groups which offer many flexible options for bioconjugation. This chapter focuses on discussing some of the approaches including periodate oxidation, carbodiimide, maleimide, and heterofunctional linkers, for conjugating antibodies to different nanocarriers. The advantages and limitations are described herein. Specific examples are selected to demonstrate the experimental procedures and to illustrate the potential for applying to other nanocarrier system.

Real time monitoring of biomaterial-mediated inflammatory responses via macrophage-targeting NIR nanoprobes

Medical implant-mediated inflammatory responses, often involving high levels of macrophages, are typically determined by histological analyses. These methods however are time consuming and require many animals to monitor the kinetics of inflammatory reactions and to generate reproducible outcomes. Recent studies have shown that activated macrophages in inflamed tissue express high levels of folate receptor (FR). In this study, FR-targeting NIR nanoprobes were fabricated and then tested for their ability to detect and quantify the extent of biomaterial-mediated inflammatory responses in vivo. Indeed, FR-targeting nanoprobes preferentially accumulate on activated macrophage surfaces. When administered intravenously, we found that the FR-targeting nanoprobes distinctively gathered in the inflamed tissues and that a different extent of FR-targeting nanoprobe gathering could be found in tissues implanted with different types of biomaterials. Most importantly, we found that there was a good relationship between the extent of inflammatory reactions and the intensity of nanoprobe-associated NIR signal in tissue. Our results support that FR-targeting NIR nanoprobes can be used to monitor and quantify the extent of macrophage recruitment and the degree of an implants' biocompatibility in real time.