Biosensors are powerful diagnostic tools defined as having a biorecognition element for analyte specificity and a transducer for a quantifiable signal. There are a variety of different biorecognition elements, each with unique characteristics. Understanding the advantages and disadvantages of each biorecognition element and their influence on overall biosensor performance is crucial in the planning stages to promote the success of novel biosensor development. Therefore, this review will focus on selecting the optimal biorecognition element in the preliminary design phase for novel biosensors. Included is a review of the typical characteristics and binding mechanisms of various biorecognition elements, and how they relate to biosensor performance characteristics, specifically sensitivity, selectivity, reproducibility, and reusability. The goal is to point toward language needed to improve the design and development of biosensors toward clinical success.

Establishing methods for controlling aspects of large amplitude submolecular movements is a prerequisite for the development of artificial devices that function through rotary motion at the molecular level. Here we demonstrate that the rate of rotation of the interlocked components of fumaramide-derived [2]rotaxanes can be accelerated, by >6 orders of magnitude, by isomerizing them to the corresponding maleamide [2]rotaxanes by using light. molecular machines ͉ dynamics L arge amplitude internal rotations that resemble to some extent processes found in authentic machinery have recently inspired analogic molecular versions of gears (1), turnstiles (2), brakes (3), ratchets (4, 5), rotors (6), and unidirectional spinning motors (7-10) and are an inherent characteristic of many catenanes and rotaxanes (11-13). Establishing methods for controlling aspects of such movements is a prerequisite for the development of artificial devices that function through rotary motion at the molecular level. In this regard, we recently reported the unexpected discovery that the rate of rotation of the interlocked components of benzylic amide macrocyclecontaining nitrone and fumaramide [2]rotaxanes can be slowed (''dampened'') by 2-3 orders of magnitude by applying a modest (Ϸ1 V⅐cm Ϫ1) external oscillating electric field (14). Here we demonstrate that the rate of rotation of the interlocked components of the olefin-based rotaxanes can also be accelerated, by Ͼ6 orders of magnitude, using another broadly useful stimulus, light.Fumaramide threads template the assembly of benzylic amide macrocycles around them to form rotaxanes in high yields (15). This cheap and simple preparative procedure (suitable threads are prepared in a single step from fumaryl chloride and a bulky primary or secondary amine) is particularly efficient because the trans-olefin fixes the two hydrogen bond-accepting groups of the thread in an arrangement that is complementary to the geometry of the hydrogen bonddonating sites of the forming macrocycle. However, the feature of the fumaramide unit that makes it such an effective template also provides an opportunity to enforce a geometrical change in the thread after rotaxane formation, thus altering the nature and strength of the interactions between the interlocked components. Isomerization of the olefin from E-to Z-must necessarily disrupt the near-ideal hydrogen bonding motif between macrocycle and thread and therefore also change any internal dynamics governed by those interactions.To test this idea, the photochemical isomerization of three fumaramide-based threads (E-1-3) and rotaxanes (E-4-6) was investigated. The synthesis of rotaxanes E-4 and E-6 has been described (15), and E-5 was prepared in analogous fashion from the corresponding thread, E-2, isophthaloyl dichloride and p-xylylene diamine (Scheme 1).** Under the same reaction conditions the cis-olefin (maleamide) threads, Z-1-3, did not give detectable quantities of the corresponding Z-rotaxanes. Experimental ProceduresGeneral Method for the Photoisomeri...

Shedding light on a mechanical event: Films of a polymer–rotaxane conjugate were cast on quartz slides, the films were covered with aluminum masks, and the unmasked areas were exposed to vapors of DMSO. The solvent induces a change in position of the macrocycle in the molecular shuttle that leads to “on” states of the rotaxane fluorescence in the unmasked areas (see image).