EDITORIAL pubs.acs.org/JPCL
Advances in Bionanotechnolgy
T
he evolution of nanotechnology in the last couple of decades has sparked an explosion in a new and rapidly developing field of nanobiology with particular applications in nanobiomedicine. The field is extremely multidisciplinary, focusing on the development of multifunctional systems, such as quantum dots (QDs), nanoshells, nanocells, and dendrimers, and subsequently the integration of biocompatibility. One day these materials will perform complex tasks with high specificity in vivo. Advances in bioimaging using various nanoparticles as well as targeted drug delivery, where specific drugs are carried on smart bionanocapsules, have the potential to make a huge impact in future healthcare, where they will be applied in the diagnosis and treatment of cancer and other diseases. Selected advances in this broad field of nanobiology, which synergetically combines physical chemistry and biology toward practical applications in medicine, are highlighted in this Editorial. Of the three Perspective articles, which encompass different fields of nanobiochemistry, one focuses on the molecular level through the employment of site-specific probes, enhancing the structural sensitivity of spectroscopic techniques for the investigation of structural and dynamical properties of biomolecules.1 The other two explore the potential of biomolecule QD hybrid systems for bioanalytical applications2 and the development of multicompartment particle assemblies for bioinspired encapsulated reactions.3 Over billions of years nature has engineered extremely complex and superbly configured biosystems on a cellular level. Gaining more insight into the cellular machinery and the finely tuned processes will ultimately allow us to devise ways of manipulating those activities in cases when their functionalities are compromised by disease. As important steps in that direction, spectroscopic techniques might allow a way to monitor the local environment of biological molecules and extract the chemical dynamics of the system of interest. Waegele et al.1 have pointed out that introduction of small chemical probes such as nitriles, thiocyanates and azides into proteins of interest would result in a minimal perturbation of the protein conformation. They stress, nonetheless, that functionalization of proteins could lead to alterations of the structure, stability and enzymatic activity of the native protein. Ideally, potential functional groups used as spectroscopic probes are characterized by a simple vibrational transition, with a relatively high extinction coefficient, which is spectrally well resolved from other vibrational modes of the proteins. What makes these groups attractive is that in addition to vibrational spectroscopy, they also possess signatures in fluorescence and NMR spectra, as Waegele et al. have illustrated through a number of examples. The choice of probe will ultimately depend on the system under study, and one of the crucial points in the field is the expansion of the library of potential site-specific spectroscopic probes to characterize an expanse of protein microenvironments in diverse biological systems. Various hybrid nanostructures, created through a bottom-up approach, have been implemented in the exploration and manipulation of cellular functions. Nanoparticles usually have a primary function, such as their ability to report their location by photoluminescence or magnetic properties suitable for contrast agents r 2011 American Chemical Society
in biomedical imaging. Special properties of nanoparticles such as enhancement of local heating can be used to kill cancer cells, or structural attributes can allow them to transport substances of interest. However, in order to render them functional in vivo, a lot of research time has been devoted to biocompatible functionalizations. To verify that these smart nanomaterials are truly “smart”, one has to consider their specificity, multimodality, efficacy, and confirm the absence of toxicity for in vivo applications. A common attribute of all nanostructures is their large surface area, which can be manipulated to achieve stability and solubility of the particle, but also allows for the incorporation of multiple diagnostics, which could be either optically or magnetically active. Researchers envision that this field is evolving toward the fabrication of multifunctional particles for integrated imaging and therapy. Formulation of hybrid sensor-carrier nanocomposites will require careful design to incorporate a smart surface coating, target moieties, and imaging probes in addition to carefully constructed single- or multicompartment capsules for drug delivery. Semiconductor QDs have emerged as fantastic probes owing to their photostability and the tunability of their emission from the visible into the infrared region of the spectrum, simply through the manipulation of their size and composition. The ability to simultaneously excite with a single light source variously sized QDs, which have been functionalized with different markers, enables imaging of multiple targets in a single experiment. A more advanced application of QDs is highlighted in the perspective by Freeman et al.,2 where biomolecule QD hybrid systems exploit clever photophysical engineering, which is harvested in bioanalytical applications. An intricate probe design was achieved through the integration of photophysical mechanisms, including F€orster resonance energy transfer (FRET), electron transfer, and chemiluminescnce resonance energy transfer, with physical properties of QDs, resulting in diverse biosensing approaches. The logistics of drug release from engineered nanostructures is yet another process that needs to be fine-tuned in order to optimize the efficacy of enzymatic therapies. It is believed that the answer lies in a second generation of carriers, whose architectural design is based on multicompartmentalization, and whose functionalities would be inspired by cellular mimicry. These controlled release reservoirs are engineered using liposomes, cubosomes, polymersomes, polymer capsules, or colloidosomes as building blocks, where combinations are assembled as to harvest their desirable properties, such as high carrying capacity, or favorable release profiles that are easier to regulate. These complex hierarchical architectures are superior to single-compartment assemblies because they have more control over confined chemical and biochemical reactions and they incorporate triggered cargo release. Chandrawati et al.3 give a comprehensive review of multicompartment particle systems in the areas of microencapsulated catalysis. These systems are inspired by biological cells, which are able to spatially separate reactive Published: October 20, 2011 2678
dx.doi.org/10.1021/jz201298k | J. Phys. Chem. Lett. 2011, 2, 2678–2679
The Journal of Physical Chemistry Letters
EDITORIAL
species in the cell interior and impeccably regulate numerous enzymatic reactions. The authors illustrate the potential of a few types of unique compartmentalized nanostructures, which could be the initial step toward the bottom-up assembly of an artificial cell. The ingenuity of researchers playing in this “nano-Legoworld” of biologically functionalized nanoblocks is truly remarkable. The proof-of-concept ideas in these Perspective articles have mainly proved to be functional in controlled conditions, but most of the applications will face the next hurdle as they are tested in chemically diverse biological environments. It is also fun to think about what the future of the field will bring. The big difference between the kinds of bioprobes and reactors designed at this time and remarkable biological components is that our synthetic systems are relatively unresponsive and static. Stability, robustness, and performance of biological systems prevails in a large part because of the exquisite engineering of control and feedback loops.4,5 All the sophisticated machines we use have these qualities engineered into them: for example, the workings of antilock brakes in a car. The next paradigm shift in functional nanoscale systems surely will be to make responsive systems that work by the principles of engineering control theory. Tihana Mirkovic and Gregory D. Scholes* Department of Chemistry, Institute for Optical Sciences, and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6 Canada
’ AUTHOR INFORMATION Corresponding Author
*E-mail address:
[email protected].
’ REFERENCES (1) Waegele, M. M.; Culik, R. M.; Gai, F. Site-Specific Spectroscopic Reporters of the Local Electric Field, Hydration, Structure, and Dynamics of Biomolecules. J. Phys. Chem. Lett. 2011, 2, 2598–2609. (2) Freeman, R.; Willner, B.; Willner, I. Integrated Biomolecule Quantum Dot Hybrid Systems for Bioanalytical Applications. J. Phys. Chem. Lett. 2011, 2, 2667–2677. (3) Chandrawati, R.; van Koeverden, M. P.; Lomas, H.; Caruso, F. Multicompartment Particle Assemblies for Bioinspired Encapsulated Reactions. J. Phys. Chem. Lett. 2011, 2, 2639–2649. (4) Csete, M. E.; Doyle, J. C. Reverse Engineering of Biological Complexity. Science 2002, 295, 1664–1669. (5) El-Samed, H.; Kurata, H.; Doyle, J. C.; Gross, C. A.; Khammash, M. Survivinh Heat Shock: Control Strategies for Robustness and Performance. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 2736–2741.
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