Abstract
Nanoparticle scaffolds can impart multiple benefits onto immobilized enzymes including enhanced stability, activity, and recoverability. The magnitude of these benefits is modulated by features inherent to the scaffold–enzyme conjugate, amongst which the size of the nanoscaffold itself can be critically important. In this review, we highlight the benefits of enzyme immobilization on nanoparticles and the factors affecting these benefits using quantum dots and gold nanoparticles as representative materials due to their maturity. We then review recent literature on the use of these scaffolds for enzyme immobilization and as a means to dissect the underlying mechanisms. Detailed analysis of the literature suggests that there is a “sweet-spot” for scaffold size and the ratio of immobilized enzyme to scaffold, with smaller scaffolds and lower enzyme:scaffold ratios generally providing higher enzymatic activities. We anticipate that ongoing studies of enzyme immobilization onto nanoscale scaffolds will continue to sharpen our understanding of what gives rise to beneficial characteristics and allow for the next important step, namely, that of translation to large-scale processes that exploit these properties.
Highlights
Enzymatic catalysis is exquisite in its ability to enhance specific reaction rates by orders of magnitude using precisely selected substrates from within a milieu of other compounds [1]
Unlike several other studies reporting the enhanced enzymatic activity at the interface of smaller rather than large NPs, Vranish et al found the greatest increase in kcat when the coupled pyruvate kinase (PykA)−lactate dehydrogenase (LDH) enzyme system colocalized on a quantum dot (QD) surface of the larger, oblong 605 QDs with length × width of 10.1 ± 1.0 nm × 4.5 ± 0.4 nm rather than the spherical 525 QDs of diameter 4.3 ±
Among NPs, QDs and AuNPs are of particular popularity, potentially due to many of their shared properties owing to their being nanocrystalline, predominantly monodispersed, with certain favorable properties, including size-tunable photoluminescence and the capacity to act as excellent FRET donors and acceptors, in the case of QDs, and surface plasmon resonance for
Summary
Enzymatic catalysis is exquisite in its ability to enhance specific reaction rates by orders of magnitude using precisely selected substrates from within a milieu of other compounds [1]. While solution-based enzymes have shown success in many applications, it can be desirable to immobilize them for a variety of reasons (highlighted below) This is evidenced by nature’s use, and researchers’ engineered exploitation, of metabolons (e.g., clustered TCA cycle enzymes) and scaffolds (e.g., cellulosomes of scaffoldin and cellulases) [3,10,11]. NPs notably present unique features for enzyme immobilization, and two in particular—quantum dots (QDs) and gold-nanoparticles (AuNPs)—will be the subject of this review. The interested reader is directed to excellent reviews on reviews on other scaffolds for enzyme immobilization [4,12,13,14]. AuNP for enhancing biocatalytic applications by reviewing the unique benefits that have already been elucidated and extending applications by reviewing thework unique benefits that and havelong already this to an outlook for future in both the near term.been elucidated and extending this to an outlook for future work in both the near and long term
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