Nearly all implantable bioelectronics are powered by bulky batteries which limit device miniaturization and lifespan. Moreover, batteries contain toxic materials and electrolytes that can be dangerous if leakage occurs. Herein, an approach to fabricate implantable protein-based bioelectrochemical capacitors (bECs) employing new nanocomposite heterostructures in which 2D reduced graphene oxide sheets are interlayered with chemically modified mammalian proteins, while utilizing biological fluids as electrolytes is described. This protein-modified reduced graphene oxide nanocomposite material shows no toxicity to mouse embryo fibroblasts and COS-7 cell cultures at a high concentration of 1600 μg mL−1 which is 160 times higher than those used in bECs, unlike the unmodified graphene oxide which caused toxic cell damage even at low doses of 10 μg mL−1. The bEC devices are 1 μm thick, fully flexible, and have high energy density comparable to that of lithium thin film batteries. COS-7 cell culture is not affected by long-term exposure to encapsulated bECs over 4 d of continuous charge/discharge cycles. These bECs are unique, protein-based devices, use serum as electrolyte, and have the potential to power a new generation of long-life, miniaturized implantable devices.

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Controlling the properties of enzymes bound to solid surfaces in a rational manner is a grand challenge. Here we show that preadsorption of cationized bovine serum albumin (cBSA) to α-Zr(IV) phosphate (α-ZrP) nanosheets promotes enzyme binding in a predictable manner, and surprisingly, the enzyme binding is linearly proportional to the number of residues present in the enzyme or its volume, providing a powerful, new predictable tool. The cBSA loaded α-ZrP (denoted as bZrP) was tested for the binding of pepsin, glucose oxidase (GOX), tyrosinase, catalase, myoglobin and laccase where the number of residues increased from the lowest value of ∼153 to the highest value of 2024. Loading depended linearly on the number of residues, rather than enzyme charge or its isoelectric point. No such correlation was seen for the binding of these enzymes to α-ZrP nanosheets without the preadsorption of cBSA, under similar conditions of pH and buffer. Enzyme binding to bZrP was supported by centrifugation studies, powder X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy. All the bound enzymes retained their secondary structure and the extent of structure retention depended directly on the amount of cBSA preadsorbed on α-ZrP, prior to enzyme loading. Except for tyrosinase, all enzyme/bZrP biocatalysts retained their enzymatic activities nearly 90-100%, and biofunctionalization enhanced the loading, improved structure retention and supported higher enzymatic activities. This approach of using a chemically modified protein to serve as a glue, with a predictable affinity/loading of the enzymes, could be useful to rationally control enzyme binding for applications in advanced biocatalysis and biomedical applications.

A rational strategy is presented here to enhance enzyme stability by gaining control over the noncovalent interactions at the enzyme–graphene interface (EGI). The charge (n) on a model enzyme, glucose oxidase (GOx), was systematically varied from −67 to +78 via chemical modification of its COOH groups with polyamines, and chemically modified GOx­(n) has been adsorbed onto graphene oxide (GO). Control of the net charge on GOx­(n) provided an excellent handle to engineer the EGI to enhance the stability of the GOx­(n)/GO biocatalyst while retaining full activity. Enzyme loading (w/w, GOx­(n) to GO) increased with increased n, and a maximum enzyme loading of 420% (w/w) was noted when n = 0; a further increase in n decreased loading. Enzymatic activities of the GOx­(n)/GO hybrids increased steadily with n, and the maximum specific activity was about 1.6 times greater than that of GOx. There has been a good correlation between the retention of enzyme secondary structure and the corresponding enzymatic activities. These indicated an unprecedented increase in kinetic stability as a function of n, measured at 40 °C, with a maximum half-life of 38 days (n = 0, +35), which is about 150 times higher than that of GOx, under the same conditions. The kinetic barrier to denaturation increased steadily from 58.7 kcal/mol for GOx to 294 kcal mol–1 for GOx­(+35)/GO and then decreased slightly with increased n. Chemical denaturation studies showed that the improved stability is not due to changes in thermodynamic stability and that the increased kinetic stability is due to an increased barrier to denaturation. Adsorption onto GO played a key role in enhancing enzyme stability, and without GO, the stability enhancements were only marginal. Thus, engineering the EGI provided exciting opportunities to generate highly stable biocatalysts that can be stored under ambient conditions, while retaining high activities, with very long lifetimes, much needed for practical applications.

Artificial antenna complexes built via self-assembly are reported here, which indicated excellent energy transfer efficiency, macroscopic organization, unprecedented thermal stability, and ease of formation.Our system consists of four fluorescent donor-acceptor dyes, double-helical DNA and cationized bovine serum albumin, all self-assembled on cover glass slips to form functional materials. These captured radiation in the range of 330-590 nm, and excitation of any of the donor dyes resulted in efficient emission from the terminal acceptor. Excitation spectra provided unequivocal proof of energy transfer via jumper dyes, and transfer was interrupted when one of the jumper dyes was omitted, another direct evidence for cascade energy transfer. The entire assembly indicated unusually high thermal stability and continued to function efficiently even after exposure to 80 C for >169 days, an important consideration for field applications. These unusually stable, high efficiency, multichromophoric, artificial antennas are the first of their kind to demonstrate self-assembled 4-dye energy cascade, converting blue photons to red photons. † Electronic supplementary information (ESI) available: Including experimental methods, characterization of modied BSA, uorescence, circular dichroism, etc. See Scheme 1 Artificial antenna complexes constructed from donors, acceptors, cationized BSA (cBSA), and DNA.This journal is