There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Platinum-based nanostructured materials: synthesis, properties, and applications.

Taking advantage of exceptional attributes, such as being easy-to-operate, economical, sensitive, portable, and simple-to-construct, in recent decades, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors.Various electrochemical devices, such as amperometric sensors, electrochemical impedance sensors, and electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications in the detection of chemical and biological targets in terms of electrochemical change of electrode interfaces.

With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well-known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity, and biocompatibility to accelerate the signal transduction but also amplify biorecognition events with specifically designed signal tags, leading to highly sensitive biosensing. Significantly, extensive research on the construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing the wide application of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects and nanoengineered and/or nanostructured materials for the rational design of biofunctionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip and paper microfluidic devices.2 With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown a great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries.

This Review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhanced electrochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are reviewed herein (Figure ​(Figure1).1). Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemical sensors and electrochemical methods to refer to other excellent literature for a broad scope in this area.3,4 However, due to the explosion of publications in this active field, we do not claim that this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out.



Figure 1

Schematic illustration of electrochemical sensors and biosensors based on nanomaterials and nanostructures, in which electrochemical sensors for small molecular, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are demonstrated.

http://pubs.acs.org/doi/pdf/10.1021/ac5039863

Electrochemical Sensors and Biosensors Based on Nanomaterials and Nanostructures

Recent developments in paper-based microfluidic devices.

The release of metals and metal-containing compounds into the environment is a growing concern in developed and developing countries, as human exposure to metals is associated with adverse health effects in virtually every organ system. Unfortunately, quantifying metals in the environment is expensive; analysis costs using certified laboratories typically exceed $100/sample, making the routine analysis of toxic metals cost-prohibitive for applications such as occupational exposure or environmental protection. Here, we report on a simple, inexpensive technology with the potential to render toxic metals detection accessible for both the developing and developed world that combines colorimetric and electrochemical microfluidic paper-based analytical devices (mPAD) in a three-dimensional configuration. Unlike previous mPADs designed for measuring metals, the device reported here separates colorimetric detection on one layer from electrochemical detection on a different layer. Separate detection layers allows ...

Multilayer Paper-Based Device for Colorimetric and Electrochemical Quantification of Metals

Paper-based analytical devices (PADs) represent a growing class of elegant, yet inexpensive chemical sensor technologies designed for point-of-use applications. Most PADs, however, still utilize some form of instrumentation such as a camera for quantitative detection. We describe here a simple technique to render PAD measurements more quantitative and straightforward using the distance of colour development as a detection motif. The so-called distance-based detection enables PAD chemistries that are more portable and less resource intensive compared to classical approaches that rely on the use of peripheral equipment for quantitative measurement. We demonstrate the utility and broad applicability of this technique with measurements of glucose, nickel, and glutathione using three different detection chemistries: enzymatic reactions, metal complexation, and nanoparticle aggregation, respectively. The results show excellent quantitative agreement with certified standards in complex sample matrices. This work provides the first demonstration of distance-based PAD detection with broad application as a class of new, inexpensive sensor technologies designed for point-of-use applications.

Simple, distance-based measurement for paper analytical devices

The field of paper-based microfluidics has experienced rapid growth over the past decade. Microfluidic paper-based analytical devices (μPADs), originally developed for point-of-care medical diagnostics in resource-limited settings, are now being applied in new areas, such as environmental analyses. Low-cost paper sensors show great promise for on-site environmental analysis; the theme of ongoing research complements existing instrumental techniques by providing high spatial and temporal resolution for environmental monitoring. This review highlights recent applications of μPADs for environmental analysis along with technical advances that may enable μPADs to be more widely implemented in field testing.

David M. Cate

Papers

Recent developments in paper-based microfluidic devices.

Multilayer Paper-Based Device for Colorimetric and Electrochemical Quantification of Metals

Simple, distance-based measurement for paper analytical devices

Paper-based analytical devices for environmental analysis

Sensitive electrochemical sensor using a graphene–polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II)