Ed using surface sensitive techniques [1,2]. An example of an experiment demanding such supramolecular structures at surfaces includes the binding of liposome-ssDNA hybrids to surface immobilized-DNA in order to detect single nucleotide polymorphism usingtotal internal reflection fluorescence (TIRF) microscopy [3]. Another example is the large-scale positioning of self-assembled functional DNA 
nanoarrays on surfaces [4], which have been used to construct arrays of quantum dots, proteins, and DNA targets. Supramolecular constructs that link micron-sized beads have been used to engineer molecular wires 22948146 and to guide the assembly of nano and microstructures [5?]. Metal wires have been fabricated by depositing metals on multi-protein and DNA constructs connecting the surfaces of two electrodes [9,10]. Single molecule techniques such as optical tweezers have enabled the kinetic and thermodynamic characterization of DNA and protein molecules, as well as their interaction [11?4].In these methods, two ends of the molecule of interest typically are manipulated by linking them to surfaces, either directly or via molecular handles. Here molecular linkages are preferably established in-situ while still being able to sustain large forces over long timescales. Different classes of linkages have been used: Antibody-antigen linkages [13], the family of Streptavidin (STV)biotin linkages [13?5], covalent disulfide linkages [14] and covalent binding proteins (HaloTag [16] or SNAP-tag [17]). Each has its own strength 1662274 and drawbacks. Antibody-antigen interactions are specific and diverse but affinities are affected by buffer condition, pH and temperature, and thus limit the experimental conditions that can be explored. Examples are Myc-AntiMyc and Dig-AntiDig. Moreover, many commercially available antibodies are polyclonal, causing variability in the force that the linkage can sustain. The Dig-AntiDig connection can be stable purchase 64849-39-4 mechanically, and has therefore been used extensively to link DNA to surfaces [13,14]. Gracillin However, this system is less suitable for interfacing to proteins, while as a steroid compound [18]. Digoxigenin is also prone to oxidation and thus can deteriorate over time [19]. Disulfide bonds are very strong but involve long preparation times (e.g. 24?8 hr for DNA-protein coupling [20]) and the molecules of interest must be resistant to redox reactions, which limits its applicability.Optical Tweezers Study of Protein-DNA HybridsThe biotin-STV interaction is one of the most broadly used, as it is strong and efficiently established. STV is one of the most stable proteins showing high resistance to temperature, urea, guanidine, and proteases [21]. This is in contrast to linkages such as HaloTag or SNAP-tag that unfold, aggregate and encourage nonspecific binding under these harsh conditions [15]. In the presence of SDS, Streptavidin 
begins to break up into monomers only at temperatures above 60uC [22]. Because of the usefulness of biotin-STV interactions, efforts have been made to engineer variants and further optimize this system. Avidin is a glycosylated and positively charged protein (at neutral pH) which usually appears as a tetrameric biotin-binding molecule. Neutravidin (NTV) is a deglycosylated form of Avidin which is developed to decrease non-specific interactions [23]. It has recently been reported that Traptavidin, a mutant of STV, dissociates biotin more than tenfold slower, has increased mechanical strength and improved thermostability [1.Ed using surface sensitive techniques [1,2]. An example of an experiment demanding such supramolecular structures at surfaces includes the binding of liposome-ssDNA hybrids to surface immobilized-DNA in order to detect single nucleotide polymorphism usingtotal internal reflection fluorescence (TIRF) microscopy [3]. Another example is the large-scale positioning of self-assembled functional DNA nanoarrays on surfaces [4], which have been used to construct arrays of quantum dots, proteins, and DNA targets. Supramolecular constructs that link micron-sized beads have been used to engineer molecular wires 22948146 and to guide the assembly of nano and microstructures [5?]. Metal wires have been fabricated by depositing metals on multi-protein and DNA constructs connecting the surfaces of two electrodes [9,10]. Single molecule techniques such as optical tweezers have enabled the kinetic and thermodynamic characterization of DNA and protein molecules, as well as their interaction [11?4].In these methods, two ends of the molecule of interest typically are manipulated by linking them to surfaces, either directly or via molecular handles. Here molecular linkages are preferably established in-situ while still being able to sustain large forces over long timescales. Different classes of linkages have been used: Antibody-antigen linkages [13], the family of Streptavidin (STV)biotin linkages [13?5], covalent disulfide linkages [14] and covalent binding proteins (HaloTag [16] or SNAP-tag [17]). Each has its own strength 1662274 and drawbacks. Antibody-antigen interactions are specific and diverse but affinities are affected by buffer condition, pH and temperature, and thus limit the experimental conditions that can be explored. Examples are Myc-AntiMyc and Dig-AntiDig. Moreover, many commercially available antibodies are polyclonal, causing variability in the force that the linkage can sustain. The Dig-AntiDig connection can be stable mechanically, and has therefore been used extensively to link DNA to surfaces [13,14]. However, this system is less suitable for interfacing to proteins, while as a steroid compound [18]. Digoxigenin is also prone to oxidation and thus can deteriorate over time [19]. Disulfide bonds are very strong but involve long preparation times (e.g. 24?8 hr for DNA-protein coupling [20]) and the molecules of interest must be resistant to redox reactions, which limits its applicability.Optical Tweezers Study of Protein-DNA HybridsThe biotin-STV interaction is one of the most broadly used, as it is strong and efficiently established. STV is one of the most stable proteins showing high resistance to temperature, urea, guanidine, and proteases [21]. This is in contrast to linkages such as HaloTag or SNAP-tag that unfold, aggregate and encourage nonspecific binding under these harsh conditions [15]. In the presence of SDS, Streptavidin begins to break up into monomers only at temperatures above 60uC [22]. Because of the usefulness of biotin-STV interactions, efforts have been made to engineer variants and further optimize this system. Avidin is a glycosylated and positively charged protein (at neutral pH) which usually appears as a tetrameric biotin-binding molecule. Neutravidin (NTV) is a deglycosylated form of Avidin which is developed to decrease non-specific interactions [23]. It has recently been reported that Traptavidin, a mutant of STV, dissociates biotin more than tenfold slower, has increased mechanical strength and improved thermostability [1.
