Streptavidin conjugation and quantification-a method evaluation for nanoparticles

Targeting Mucin Protein Enables Rapid and Efficient Ovarian Cancer Cell Capture: Role of Nanoparticle Properties in Efficient Capture and Culture

The development of specific and sensitive immunomagnetic cell separation nanotechnologies is central to enhancing the diagnostic relevance of circulating tumor cells (CTCs) and improving cancer patient outcomes. The limited number of specific biomarkers used to enrich a phenotypically diverse set of CTCs from liquid biopsies has limited CTC yields and purity. The ultra-high molecular weight mucin, mucin16 (MUC16) is shown to physically shield key membrane proteins responsible for activating immune responses against ovarian cancer cells and may interfere with the binding of magnetic nanoparticles to popular immunomagnetic cell capture antigens. MUC16 is expressed in ≈90% of ovarian cancers and is almost universal in High Grade Serous Epithelial Ovarian Cancer. This work demonstrates that cell bound MUC16 is an effective target for rapid immunomagnetic extraction of expressor cells with near quantitative yield, high purity and viability from serum. The results provide a mechanistic insight into the effects of nanoparticle physical properties and immunomagnetic labeling on the efficiency of immunomagnetic cell isolation. The growth of these cells has also been studied after separation, demonstrating that nanoparticle size impacts cell-particle behavior and growth rate. These results present the successful isolation of "masked" CTCs enabling new strategies for the detection of cancer recurrence and select and monitor chemotherapy.

Revisiting carboxylic group functionalization of silica sol-gel materials

The carboxylic chemical group is a ubiquitous moiety present in amino acids, a ligand for transition metals, a colloidal stabilizer, and a weak acidic ion-exchanger in polymeric resins and given this property, it is attractive for responsive materials or nanopore-based gating applications. As the number of uses increases, subtle requirements are imposed on this molecular group when anchored to various platforms for the functioning of an integrated chemical system. In this context, silica stands as an inert and multipurpose platform that enables the anchoring of multiple chemical entities combined through several orthogonal synthesis methods on the interface. Surface chemical modification relies on the use of organoalkoxysilanes that must meet the demand of tuned chemical properties; this, in turn, urges for innovative approaches for having an improved, but simple, organic toolbox. Starting from commonly available molecular precursors, several approaches have emerged: hydrosilylation, click thiol-ene additions, the use of carbodiimides or the reaction between cyclic anhydrides and anchored amines. In this review, we analyze the importance of the COOH groups in the area of materials science and the commercial availability of COOH-based silanes and present new approaches for obtaining COOH-based organoalkoxide precursors. Undoubtedly, this will attract widespread interest for the ultimate design of highly integrated chemical platforms.

Size and macromolecule stabilizer-dependent performance of gold colloids in immuno-PCR

Gold nanoparticles (GNPs) are well-documented for their size and surface chemistry-dependent electronic and optical properties that are extensively utilized to develop highly sensitive immunoassays. GNP-based immuno-polymerase chain reaction (immuno-PCR) is especially interesting due to the facile loading of biomolecules on the surface of GNP probes and has been utilized to develop analyte-specific assays. In this study, the role of size and surface chemistry of GNPs is explored in detail to develop a highly sensitive and reproducible immuno-PCR assay for specific detection of biotinylated analytes. Our results indicate that smaller-sized gold nanoparticles outperform the larger ones in terms of their sensitivity in immuno-PCR assay and show superior loading of proteins and oligonucleotides on the surface of nanoparticles. Furthermore, the role of different macromolecular stabilizers (such as polyethylene glycol (PEG), bovine serum albumin (BSA), and PEGylated BSA) was compared to optimize the loading of biomolecules and to improve the signal-to-noise ratio of GNP probes. mPEG-BSA-functionalized GNP probes of 15 nm were found to be highly sensitive at low concentrations of analytes and significantly (~ 30 fold) improve the limit of detection of analytes in comparison with ELISA assay.

A quantitative view on multivalent nanomedicine targeting

Although the concept of selective delivery has been postulated over 100 years ago, no targeted nanomedicine has been clinically approved so far. Nanoparticles modified with targeting ligands to promote the selective delivery of therapeutics towards a specific cell population have been extensively reported. However, the rational design of selective particles is still challenging. One of the main reasons for this is the lack of quantitative theoretical and experimental understanding of the interactions involved in cell targeting. In this review, we discuss new theoretical models and experimental methods that provide a quantitative view of targeting. We show the new advancements in multivalency theory enabling the rational design of super-selective nanoparticles. Furthermore, we present the innovative approaches to obtain key targeting parameters at the single-cell and single molecule level and their role in the design of targeting nanoparticles. We believe that the combination of new theoretical multivalent design and experimental methods to quantify receptors and ligands aids in the rational design and clinical translation of targeted nanomedicines.

Functionalization of hybrid surface microparticles for in vitro cellular antigen classification

Hybrid material surfaces on microparticles are emerging as vehicles for many biomedical multiplexing applications. Functionalization of these hybrid surface microparticles to biomolecules presents unique challenges related to optimization of surface chemistries including uniformity, repeatability, and sample sparring. Hybrid interfaces between microlevel surfaces and individual biomolecules will provide different microenvironments impacting the surface functionalization optimization and efficiency. Here, we propose and validate the first demonstration of streptavidin adsorption-based antibody functionalization on unmodified, hybrid surface microparticles for in vitro analysis. We test this analytical technique and fabricate hybrid surface microparticles with a polystyrene core and aluminum oxide semi-coating. Additionally, we optimize the streptavidin-biotin functionalization chemistry in both assay implementation and sample sparring via analytical mass balances for these microparticles and subsequently conjugate anti-human CD11b antibodies. Result confirmation and characterization occurs from ultraviolet protein absorbance and ImageJ processing of fluorescence microscopy images. Additionally, we design and implement the multi-sectional imaging (MSI) approach to support functionalization uniformity on the hybrid surface microparticles. Finally, as a proof-of-concept performance, we validate anti-CD11b antibodies functionalization by visualizing hybrid surface microparticles conjugate to human neutrophils isolated from blood samples collected from potentially septic patients. Our study introduces and defines a category of functionalization for hybrid surface microparticles with the intent of minuscule sample volumes, low cost, and low environmental impact to be used for many cellular or proteomic in vitro multiplexing applications in the future. Graphical abstract.

Substitution pattern controlled aggregation-induced emission in donor-acceptor-donor dyes with one and two propeller-like triphenylamine donors

We present a comparative study of the spectroscopic properties of the donor-acceptor-donor substituted dyes triphenylamine-allylidenemalononitrile-julolidine (TMJ) and triphenylamine-allylidenemalononitrile-triphenylamine (TMT), bearing one and two propeller-like triphenylamine donor moieties, in solvents of varying polarity and viscosity and in the aggregated and solid state. Our results reveal control of the aggregation-induced spectroscopic changes and the packing motifs of the dye molecules in the solid state by the chemical nature and structure of the second nitrogen-containing donor, i.e., a planar and a rigid julolidine or a twisted triphenyl group. Assuming that the TMT and TMJ aggregates show a comparable arrangement of the molecules to the respective crystals, these different molecular interactions in the solid state are responsible for aggregation induced emission (AIE) in the case of TMT and its absence for TMJ. Moreover, a versatile strategy for the fluorescence enhancement of only weakly emissive AIE dyes is shown, turning these dyes into bright nanoscale fluorescent reporters by using them as stains for preformed polymer particles.

Engineering magnetic nanoparticles and their integration with microfluidics for cell isolation

Isolation of cancer cells, bacteria, and viruses from peripheral blood has important applications in cancer diagnosis, therapy monitoring, and drug development. Magnetic particles functionalized with antibodies that target receptors of cancer cells have been shown to isolate such entities using magnetic field gradients. Here, we report enhancement in capture efficiency and specificity by engineering magnetic nanoparticles and integrating them with microfluidics for the enumeration of tumor cells. Nanoparticles were made from iron oxide, coated with poly(ethylene glycol), and conjugated through avidin-biotin chemistry with antibody specifically against epithelial cell adhesion molecule (EpCAM). On exposure of targeted nanoparticles to tumor cells, specific uptake by EpCAM-expressing tumor cells (e.g., BxPC3, a pancreatic cancer cell) was observed, whereas there was negligible uptake by cells with low EpCAM expression (e.g., CCRF-CEM, a leukemia cell). Using an arrangement of magnets called a Halbach array, capture efficiency and specificity towards BxPC3 cells tagged with magnetic nanoparticles were enhanced, compared to conditions without the magnetic field gradient and/or without magnetic nanoparticles, either in buffer or in whole blood. These results illustrate that engineered magnetic nanoparticles and their integration with microfluidics have great potential for tumor cell enumeration and cancer prognosis.

Multimodal Cleavable Reporters for Quantifying Carboxy and Amino Groups on Organic and Inorganic Nanoparticles

Organic and inorganic nanoparticles (NPs) are increasingly used as drug carriers, fluorescent sensors, and multimodal labels in the life and material sciences. These applications require knowledge of the chemical nature, total number of surface groups, and the number of groups accessible for subsequent coupling of e.g., antifouling ligands, targeting bioligands, or sensor molecules. To establish the concept of catch-and-release assays, cleavable probes were rationally designed from a quantitatively cleavable disulfide moiety and the optically detectable reporter 2-thiopyridone (2-TP). For quantifying surface groups on nanomaterials, first, a set of monodisperse carboxy-and amino-functionalized, 100 nm-sized polymer and silica NPs with different surface group densities was synthesized. Subsequently, the accessible functional groups (FGs) were quantified via optical spectroscopy of the cleaved off reporter after its release in solution. Method validation was done with inductively coupled plasma optical emission spectroscopy (ICP-OES) utilizing the sulfur atom of the cleavable probe. This comparison underlined the reliability and versatility of our probes, which can be used for surface group quantification on all types of transparent, scattering, absorbing and/or fluorescent particles. The correlation between the total and accessible number of FGs quantified by conductometric titration, qNMR, and with our cleavable probes, together with the comparison to results of conjugation studies with differently sized biomolecules reveal the potential of catch-and-release reporters for surface analysis. Our findings also underline the importance of quantifying particularly the accessible amount of FGs for many applications of NPs in the life sciences.

Surface Modifications for Photon-Upconversion-Based Energy-Transfer Nanoprobes

An emerging class of inorganic optical reporters are near-infrared (NIR) excitable lanthanide-based upconversion nanoparticles (UCNPs) with multicolor emission and long luminescence lifetimes in the range of several hundred microseconds. For the design of chemical sensors and optical probes that reveal analyte-specific changes in their spectroscopic properties, these nanomaterials must be combined with sensitive indicator dyes that change their absorption and/or fluorescence properties selectively upon interaction with their target analyte, utilizing either resonance energy transfer (RET) processes or reabsorption-related inner filter effects. The rational development of UCNP-based nanoprobes for chemical sensing and imaging in a biological environment requires reliable methods for the surface functionalization of UCNPs, the analysis and quantification of surface groups, a high colloidal stability of UCNPs in aqueous media as well as the chemically stable attachment of the indicator molecules, and suitable instrumentation for the spectroscopic characterization of the energy-transfer systems and the derived nanosensors. These topics are highlighted in the following feature article, and examples of functionalized core-shell nanoprobes for the sensing of different biologically relevant analytes in aqueous environments will be presented. Special emphasis is placed on the intracellular sensing of pH.