The successful growth of colloidal lead halide perovskite quantum dots (PQDs) has generated tremendous interest in the community, due to the unique properties and the promise PQDs offer for use in applications involving light-emitting devices and solar cell technology. However, tangible progress in probing their fundamental properties and/or their integration into optoelectronic devices has been hampered by issues of colloidal and photophysical instability. Here, we introduce a promising surface coating strategy relying on a polyzwitterion polymer, where high-affinity binding onto the QDs is driven by multicoordinating electrostatic interactions with the ion-rich surfaces of CsPbBr3 PQDs. The polymer ligands were synthesized by installing a stoichiometric mixture of amine-modified sulfobetaine anchors and solubilizing motifs on poly­(isobutylene-alt-maleic anhydride), PIMA, via nucleophilic addition reaction. We find that this coating approach imparts enhanced colloidal and photophysical stability to the nanocrystals over a broad range of solvent conditions and in powder form. This approach also allows easy phase transfer of the PQDs from nonpolar media to an array of solutions with varying polarities and properties. Additionally, the stabilization strategy preserves the photophysical and structural characteristics of the nanocrystals over a period extending to 1.5 years under certain conditions.

The transmission of SARS-CoV-2 coronavirus has led to the COVID-19 pandemic. Nucleic acid testing while specific has limitations for mass surveillance. One alternative is the main protease (M pro ) due to its functional importance in mediating the viral life cycle. Here, we describe a combination of modular substrate and gold colloids to detect M pro via visual readout. The strategy involves zwitterionic peptide that carries opposite charges at the C-/N-terminus to exploit the specific recognition by M pro . Autolytic cleavage releases a positively charged moiety that assembles the nanoparticles with rapid color changes (t < 10 min). We determine a limit of detection for M pro in breath condensate matrices < 10 nM. We further assayed ten COVID-negative subjects and found no false-positive result. In the light of simplicity, our test for viral protease is not limited to an equipped laboratory, but also is amenable to integrating as portable point-of-care devices including those on face-coverings.

Reacting poly­(maleic anhydride)-based polymers with H2N–R nucleophiles is a flexible and highly effective approach for preparing a variety of multifunctional, multicoordinating, and multireactive polymers. The exact transformation of the anhydride ring during this addition reaction is still an open question. In this report, we characterize the transformation of a representative block copolymer, poly­(isobutylene-alt-maleic anhydride), with a few H2N–R nucleophiles. In particular, we test the effects of varying a few reaction parameters/conditions (e.g., temperature, solvent, reaction time, and addition of thionyl chloride) on the nature of the anhydride transformation and bond formed between the polymer and the lateral R groups. The resulting polymers are characterized using a combination of analytical techniques including FT-IR, one- and two-dimensional NMR, and gel electrophoresis. We find that the ring opening transformation occurs under mild conditions. Conversely, cyclic imide transformation can take place for reactions carried out at high temperature (e.g., in DMF under refluxing conditions). We also find that use of a protic solvent, such as methanol, or addition of thionyl chloride (SOCl2) to the reaction mixture under refluxing conditions can promote cyclic imide transformation. The cyclic imide transformation is nonetheless partial, as carboxyl groups could still be accounted for in the resulting compounds. Depending on the type of transformation, the resulting polymer can exhibit a few distinct properties, such as net charge buildup along the chain, or the appearance of weak UV–vis absorption and fluorescence properties. These findings are useful for understanding the properties exhibited by polymer materials prepared via this flexible and highly effective route using anhydride containing polymers and oligomers.

There is a need for surveillance of COVID-19 to identify individuals infected with SARS-CoV-2 coronavirus. Although specific, nucleic acid testing has limitations in terms of point-of-care testing. One potential alternative is the nonstructural protease (nsp5, also known as M pro /3CL pro ) implicated in SARS-CoV-2 viral replication but not incorporated into virions. Here, we report a divalent substrate with a novel design, (Cys) 2 –(AA) x –(Asp) 3 , to interface gold colloids in the specific presence of M pro leading to a rapid and colorimetric readout. Citrate- and tris(2-carboxyethyl)phosphine (TCEP)-AuNPs were identified as the best reporter out of the 17 ligated nanoparticles. Furthermore, we empirically determined the effects of varying cysteine valence and biological media on the sensor specificity and sensitivity. The divalent peptide was specific to M pro , that is, there was no response when tested with other proteins or enzymes. Furthermore, the M pro detection limits in Tris buffer and exhaled breath matrices are 12.2 and 18.9 nM, respectively, which are comparable to other reported methods (i.e., at low nanomolar concentrations) yet with a rapid and visual readout. These results from our work would provide informative rationales to design a practical and noninvasive alternative for COVID-19 diagnostic testing—the presence of viral proteases in biofluids is validated.

A novel core–shell magnetic fibrous nanocatalyst, Pd/Fe3O4@SiO2@KCC-1 with easily accessible active sites and a convenient recovery property, was successfully developed.