Biofunctionalization of Multiplexed Silicon Photonic Biosensors

Silicon photonic (SiP) sensors offer a promising platform for robust and low-cost decentralized diagnostics due to their high scalability, low limit of detection, and ability to integrate multiple sensors for multiplexed analyte detection. Their CMOS-compatible fabrication enables chip-scale miniaturization, high scalability, and low-cost mass production. Sensitive, specific detection with silicon photonic sensors is afforded through biofunctionalization of the sensor surface; consequently, this functionalization chemistry is inextricably linked to sensor performance. In this review, we first highlight the biofunctionalization needs for SiP biosensors, including sensitivity, specificity, cost, shelf-stability, and replicability and establish a set of performance criteria. We then benchmark biofunctionalization strategies for SiP biosensors against these criteria, organizing the review around three key aspects: bioreceptor selection, immobilization strategies, and patterning techniques. First, we evaluate bioreceptors, including antibodies, aptamers, nucleic acid probes, molecularly imprinted polymers, peptides, glycans, and lectins. We then compare adsorption, bioaffinity, and covalent chemistries for immobilizing bioreceptors on SiP surfaces. Finally, we compare biopatterning techniques for spatially controlling and multiplexing the biofunctionalization of SiP sensors, including microcontact printing, pin- and pipette-based spotting, microfluidic patterning in channels, inkjet printing, and microfluidic probes.

An Improved Protocol for the Stereoselective Synthesis of β-d-Glycosyl Fluorides from 2-O-Acyl Thioglycosides

A safe and operationally simple protocol for the preparation of β-d-glycosyl fluorides is presented. We demonstrate that a precise combination of XtalFluor-M, N-bromosuccinimide, and Et₃N·3HF can mediate facile, high-yielding, and diastereoselective conversions of 2-O-acyl thioglycosides to β-d- and other 1,2-trans glycosyl fluorides. The key roles of these reagents are dissected in this work, as is the impact of their interplay on the fluorination stereoselectivity.

Glycosyl Formates: Glycosylations with Neighboring-Group Participation

Protected 2-O-benzyolated glycosyl formates were synthesized in one-step from the corresponding orthoester using formic acid as the sole reagent. Glucopyranosyl, mannopyranosyl and galactopyranosyl donors were synthesized and their glycosylation properties studied using model glycosyl acceptors of varied steric bulk and reactivity. Bismuth triflate was the preferred catalyst and KPF₆ was used as an additive. The 1,2-trans-selectivities resulting from neighboring-group participation were excellent and the glycosylations were generally high-yielding.

Functionalization and Patterning of Self-Assembled Monolayers and Polymer Brushes Using Microcontact Chemistry

Because the surface connects a material to its environment, the functionalization, modification, and patterning of surfaces is key to a wide range of materials applied in microelectronics, displays, sensing, microarrays, photovoltaics, catalysis, and other fields. Self-assembled monolayers (SAMs), which can be deposited on a wide range of inorganic materials, are only a few nanometers thick, yet they can radically change the properties of the resulting interface. Alternatively, thin polymer films composed of polymer brushes grown from the surface provide a more robust molecular modification of inorganic materials. For many applications, patterned SAMs or polymer brushes are desired. Over the past decade, our group has shown that both SAMs as well as polymer brushes can be patterned very efficiently using microcontact printing. In microcontact printing, a molecular "ink" is deposited on a suitable substrate using a microstructured elastomer stamp, which delivers the ink exclusively in the area of contact between stamp and substrate. In contrast to most types of lithography, microcontact printing does not require expensive equipment. Our work has shown that "microcontact chemistry" is a powerful additive surface patterning method, in which molecular inks react with a precursor SAM during printing so that surfaces can be modified with various orthogonal functional groups or molecular recognition sites in microscale patterns. Functional groups include reactive groups for click chemistry or photochemistry and initiators for radical polymerization. Molecular recognition sites include host-guest chemistry as well as biochemical ligands such as carbohydrates and biotin. In this Account, we present an overview of our research in this area including selected examples of work by other groups. In the first part, we review our work on the patterning of SAMs using microcontact chemistry, with a focus on click chemistry and photochemistry. We will show how cycloadditions, thiol-ene reactions, and tetrazole chemistry can be used to obtain versatile surface patterns. In the second part, we demonstrate that microcontact chemistry can be used to pattern polymer brushes. Among others, initiators for surface-induced nitroxide-mediated polymerization and atom transfer polymerization were printed and used to grow patterned polymer brushes with molecular recognition groups suitable for responsive surface adhesion. In the third part, we describe how SAMs and polymer brushes can be printed on microparticles instead of flat substrates so that Janus particles with functional patches can be obtained. Finally, we present a brief outlook on further developments expected in this field.