Sisi Cao

Polydopamine-filled bacterial nanocellulose as a biodegradable interfacial photothermal evaporator for highly efficient solar steam generation

Solar steam generation by heat localization is considered to be a highly efficient, sustainable way to alleviate water shortage in resource-limited regions. However, most of the interfacial photothermal evaporators demonstrated so far involve non-biodegradable nanoscale materials, which can quickly pose a significant threat to the environment and ecosystems, especially marine ecosystems, after their disposal. For the first time, a flexible, scalable and, more importantly, completely biodegradable photothermal evaporator for highly efficient solar steam generation is introduced. The bilayered evaporator is comprised of bacterial nanocellulose (BNC) densely loaded with polydopamine (PDA) particles during its growth. The biodegradable foam introduced here exhibits large light absorption and photothermal conversion, heat localization, and efficient water transportation, leading to an excellent solar steam generation performance under one sun (efficiency of ∼78%). The novel material and scalable process demonstrated here can be a sustainable solution to alleviate the global water crisis.

Plasmonic Nanogels for Unclonable Optical Tagging

We demonstrate the fabrication of novel functional gel coatings with randomized physical and chemical patterns that enable dual encoding ability to realize unclonable optical tags. This design is based on swelling-mediated massive reconstruction of an ultrathin responsive gelatinous polymer film uniformly adsorbed with plasmonic nanostructures into a randomized network of interacting folds, resulting in bright electromagnetic hotspots within the folds. We reveal a strong correlation between the topology and near-field electromagnetic field enhancement due to the intimate contact between two plasmonic surfaces within the folds, each of them representing a unique combination of local topography and chemical distribution caused by the formation of electromagnetic hotspots. Because of the efficient trapping of the Raman reporters within the uniquely distributed electromagnetic hotspots, the surface enhanced Raman scattering enhancement from the morphed plasmonic gel was found to be nearly 40 times higher compared to that from the pristine plasmonic gel. Harnessing the nondeterministic nature of the folds, the folded plasmonic gel can be employed as a multidimensional (with dual topo-chemical encoding) optical taggant for prospective anticounterfeiting applications. Such novel optical tags based on the spontaneous folding process are virtually impossible to replicate because of the combination of nondeterministic physical patterns and chemical encoding.

Rapid, Point‐of‐Care, Paper‐Based Plasmonic Biosensor for Zika Virus Diagnosis

Zika virus (ZIKV) is an increasing global health challenge. There is an urgent need for rapid, low‐cost, and accurate diagnostic tests that can be broadly distributed and applied in pandemic regions. Here, an innovative, adaptable, and rapidly deployable bioplasmonic paper‐based device (BPD) is demonstrated for the detection of ZIKV infection, via quantification of serum anti‐ZIKV‐nonstructural protein 1 (NS1) IgG and IgM. BPD is based on ZIKV‐NS1 protein as a capture element and gold nanorods as plasmonic nanotransducers. The BPD displays excellent sensitivity and selectivity to both anti‐ZIKV‐NS1 IgG and IgM in human serum. In addition, excellent stability of BPDs at room and even elevated temperature for one month is achieved by metal–organic framework (MOF)‐based biopreservation. MOF‐based preservation obviates the need for device refrigeration during transport and storage, thus enabling their use in point‐of‐care and resource‐limited settings for ZIKV surveillance. Furthermore, the versatile design (interchangeable recognition element) of BPDs more generally enables their ready adaptation to diagnose other emerging infectious diseases.

Metal-Organic Framework Encapsulation for the Preservation and Photothermal Enhancement of Enzyme Activity

Interfacing biomolecules with functional materials is a key strategy toward achieving externally-triggered biological function. The rational integration of functional proteins, such as enzymes, with plasmonic nanostructures that exhibit unique optical properties such as photothermal effect provides a means to externally control the enzyme activity. However, due to the labile nature of enzymes, the photothermal effect of plasmonic nanostructures is mostly utilized for the enhancement of the biocatalytic activity of thermophilic enzymes. In order to extend and utilize the photothermal effect to a broader class of enzymes, a means to stabilize the immobilized active protein is essential. Inspired by biomineralization for the encapsulation of soft tissue within protective exteriors in nature, metal-organic framework is utilized to stabilize the enzyme. This strategy provides an effective route to enhance and externally modulate the biocatalytic activity of enzymes bound to functional nanostructures over a broad range of operating environments that are otherwise hostile to the biomolecules.

Add-on plasmonic patch as a universal fluorescence enhancer

Fluorescence-based techniques are the cornerstone of modern biomedical optics, with applications ranging from bioimaging at various scales (organelle to organism) to detection and quantification of a wide variety of biological species of interest. However, the weakness of the fluorescence signal remains a persistent challenge in meeting the ever-increasing demand to image, detect, and quantify biological species with low abundance. Here, we report a simple and universal method based on a flexible and conformal elastomeric film with adsorbed plasmonic nanostructures, which we term a “plasmonic patch,” that provides large (up to 100-fold) and uniform fluorescence enhancement on a variety of surfaces through simple transfer of the plasmonic patch to the surface. We demonstrate the applications of the plasmonic patch in improving the sensitivity and limit of detection (by more than 100 times) of fluorescence-based immunoassays implemented in microtiter plates and in microarray format. The novel fluorescence enhancement approach presented here represents a disease, biomarker, and application agnostic ubiquitously applicable fundamental and enabling technology to immediately improve the sensitivity of existing analytical methodologies in an easy-to-handle and cost-effective manner, without changing the original procedures of the existing techniques.Fluorescence: Stick-on patch fixes weak bio-signalsAdding a stretchy, nanoparticle-embedded elastomer onto standard fluorescence-based immunoassays raises biomarker signal intensities by two orders of magnitude. Nanomaterials such as gold nanorods have strong surface electromagnetic fields that can couple to the emission of a biomolecule’s fluorescent labels and enhance them, but only at certain distances apart. Srikanth Singamaneni, Rajesh Naik, and co-workers at the Washington University in St. Louis, U.S.A. have now put these nanoparticles into thin polydimethylsiloxane sheet to achieve optimal, atom-level contact for plasmonic enhancement on a variety of substrates. Because the patch is attached to immunoassays after analytical steps including antigen capture and fluorescent labeling have occurred, it avoids interfering with well-established technology. As an example, the team showed that biomarkers for kidney injury and disease could be detected at exceptionally low femtogram concentrations in urine samples.

Photothermally Active Reduced Graphene Oxide/Bacterial Nanocellulose Composites as Biofouling-Resistant Ultrafiltration Membranes

Biofouling poses one of the most serious challenges to membrane technologies by severely decreasing water flux and driving up operational costs. Here, we introduce a novel anti-biofouling ultrafiltration membrane based on reduced graphene oxide (RGO) and bacterial nanocellulose (BNC), which incoporates GO flakes into BNC in situ during its growth. In contrast to previously reported GO-based membranes for water treatment, the RGO/BNC membrane exhibited excellent aqueous stability under environmentally relevant pH conditions, vigorous mechanical agitation/sonication, and even high pressure. Importantly, due to its excellent photothermal property, under light illumination, the membrane exhibited effective bactericidal activity, obviating the need for any treatment of the feedwater or external energy. The novel design and in situ incorporation of the membranes developed in this study present a proof-of-concept for realizing new, highly efficient, and environmental-friendly anti-biofouling membranes for water purification.

Metal-Organic Framework Encapsulation Preserves the Bioactivity of Protein Therapeutics

Protein therapeutics are prone to lose their structure and bioactivity under various environmental stressors. This study reports a facile approach using a nanoporous material, zeolitic imidazolate framework-8 (ZIF-8), as an encapsulant for preserving the prototypic protein therapeutic, insulin, against different harsh conditions that may be encountered during storage, formulation, and transport, including elevated temperatures, mechanical agitation, and organic solvent. Both immunoassay and spectroscopy analyses demonstrate the preserved chemical stability and structural integrity of insulin offered by the ZIF-8 encapsulation. Biological activity of ZIF-8-preserved insulin after storage under accelerated degradation conditions (i.e., 40 °C) is evaluated in vivo using a diabetic mouse model, and shows comparable bioactivity to refrigeration-stored insulin (-20 °C). It is also demonstrated that ZIF-8-preserved insulin has low cytotoxicity in vitro and does not cause side effects in vivo. Furthermore, ZIF-8 residue can be completely removed by a simple purification step before insulin administration. This biopreservation approach is potentially applicable to diverse protein therapeutics, thus extending the benefits of advanced biologics to resource-limited settings and underserved populations/regions.