The bioorthogonal cycloaddition reaction between tetrazine and trans-cyclooctene (TCO) is rapidly growing in use for molecular imaging and cell-based diagnostics. We have surprisingly uncovered that the majority of TCOs conjugated to monoclonal antibodies using standard amine-coupling procedures are non-reactive. We show that antibody-bound TCOs are not inactivated by trans-cis isomerization and that the bulky cycloaddition reaction is not sterically hindered. Instead, TCOs are likely masked by hydrophobic interactions with the antibody. We show that introducing TCO via hydrophilic polyethyleneglycol (PEG) linkers can fully preserve reactivity, resulting in >5-fold enhancement in functional density without affecting antibody binding. This is accomplished using a novel dual bioorthogonal approach in which heterobifunctional dibenzylcyclooctyne (DBCO)-PEG-TCO molecules are reacted with azido-antibodies. Improved imaging capabilities are demonstrated for different cancer biomarkers using tetrazine-modified fluorophore and quantum dot probes. We believe that the PEG linkers prevent TCOs from burying within the antibody during conjugation, which could be relevant to other bioorthogonal tags and biomolecules. We expect the improved TCO reactivity obtained using the reported methods will significantly advance bioorthogonal pretargeting applications.

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Single cell secretion studies have provided valuable insight into population heterogeneity, but low detection sensitivity requires cells to secrete thousands of molecules. We employed semiconductor quantum dots and a new single particle imaging approach to improve detection sensitivity to only a few secreted molecules per cell.

Secreted proteins play a major role in orchestrating the response of cell populations. However, a quantitative understanding of the dynamic changes in protein secretion in response to microenvironmental cues at the single cell level remains elusive. Measurements taken using traditional molecular techniques typically require bulk cultures, and therefore cannot capture the diversity within cell populations. Recent advances in chip-based technologies have shown that single cell measurements can provide important insights into the temporal dynamics of cellular activation and function, but these tools have had limited control of the adhesive cellular microenvironment. Here, we created a single cell cytokine detection platform that allows for controlled physical and adhesive microenvironment. We validated the platform by examining cytokine secretion of macrophages exposed to varying dosages of soluble stimulation and on different adhesive substrates. We also used the platform to demonstrate that cell shape affects single macrophage cytokine secretion. Together, these results show the ability of the microwell system to detect secreted cytokines from individual macrophages in controlled adhesive environments. This technique may be broadly applied to detect secreted products from any adherent cell type.

Bioorthogonal chemistries are covalent reaction pairs that proceed in the presence of biological components with complete specificity. A suite of reactions has been described to date that provides scientists and engineers with diverse operational characteristics for different applications. Nanomaterials in particular have benefitted from these new capabilities, resulting in improved coupling efficiencies and multifunctionality. In this review, we will discuss the application of bioorthogonal chemistries to different nanomaterial systems, highlighting the advantages and limitations for use in bioconjugation. We will also describe how recent improvements in the reaction speed of catalyst-free bioorthogonal chemistries have enabled the successful coupling of nanomaterials directly to live cells. Using a recently developed reaction pair, tetrazine and trans -cyclooctene, the direct covalent coupling to cells has been shown to occur on time-scales that are relevant for biological studies and diagnostic applications and can even amplify nanomaterial binding greater than tenfold relative to traditional immunoconjugates. This powerful technique still maintains exquisite specificity, however, yielding robust results in clinical diagnostic applications using human tissue and blood samples. Future work will likely focus on further advancement of the in situ amplification technique, such as increasing nanomaterial binding, enabling multiplexed detection through the use of orthogonal reaction systems and extension to applications in vivo .

No abstract

The targeted delivery of nanoparticle carriers holds tremendous potential to transform the detection and treatment of diseases. A major attribute of nanoparticles is the ability to form multiple bonds with target cells, which greatly improves the adhesion strength. However, the multivalent binding of nanoparticles is still poorly understood, particularly from a dynamic perspective. In previous experimental work, we studied the kinetics of nanoparticle adhesion and found that the rate of detachment decreased over time. Here, we have applied the adhesive dynamics simulation framework to investigate binding dynamics between an antibody-conjugated, 200-nm-diameter sphere and an ICAM-1-coated surface on the scale of individual bonds. We found that nano adhesive dynamics (NAD) simulations could replicate the time-varying nanoparticle detachment behavior that we observed in experiments. As expected, this behavior correlated with a steady increase in mean bond number with time, but this was attributed to bond accumulation only during the first second that nanoparticles were bound. Longer-term increases in bond number instead were manifested from nanoparticle detachment serving as a selection mechanism to eliminate nanoparticles that had randomly been confined to lower bond valencies. Thus, time-dependent nanoparticle detachment reflects an evolution of the remaining nanoparticle population toward higher overall bond valency. We also found that NAD simulations precisely matched experiments whenever mechanical force loads on bonds were high enough to directly induce rupture. These mechanical forces were in excess of 300 pN and primarily arose from the Brownian motion of the nanoparticle, but we also identified a valency-dependent contribution from bonds pulling on each other. In summary, we have achieved excellent kinetic consistency between NAD simulations and experiments, which has revealed new insights into the dynamics and biophysics of multivalent nanoparticle adhesion. In future work, we will leverage the simulation as a design tool for optimizing targeted nanoparticle agents.

Recent advances in high-parameter spatial biology have yielded a rapidly growing new class of biological data, allowing researchers to more comprehensively characterize cellular state and morphology in native tissue context. However, spatial biology lacks a cohesive data abstraction on which to build novel computational tools and algorithms, making it difficult to fully leverage these emergent data. Here, we present emObject, a domain-specific data abstraction for spatial biology data and experiments. We demonstrate the simplicity, flexibility, and extensibility of emObject for a range of spatial omics data types, including the analysis of Visium, MIBI, and CODEX data, as well as for integrated spatial multiomic experiments. The development of emObject is an essential step towards building a unified data science ecosystem for spatial biology and accelerating the pace of scientific discovery.