Functional DNA nanotube arrays: bottom-up meets top-down

Nature-Inspired Thylakoid-Based Photosynthetic Nanoarchitectures for Biomedical Applications

"Drawing inspiration from nature" offers a wealth of creative possibilities for designing cutting-edge materials with improved properties and performance. Nature-inspired thylakoid-based nanoarchitectures, seamlessly integrate the inherent structures and functions of natural components with the diverse and controllable characteristics of nanotechnology. These innovative biomaterials have garnered significant attention for their potential in various biomedical applications. Thylakoids possess fundamental traits such as light harvesting, oxygen evolution, and photosynthesis. Through the integration of artificially fabricated nanostructures with distinct physical and chemical properties, novel photosynthetic nanoarchitectures can be catalytically generated, offering versatile functionalities for diverse biomedical applications. In this article, an overview of the properties and extraction methods of thylakoids are provided. Additionally, the recent advancements in the design, preparation, functions, and biomedical applications of a range of thylakoid-based photosynthetic nanoarchitectures are reviewed. Finally, the foreseeable challenges and future prospects in this field is discussed.

DNA liquid crystals with AIE effect toward humidity-indicating biomaterials

In this study, by fabricating DNA doped with tetraphenylethene-containing ammonium surfactant, the resulting solvent-free DNA ionic complex could undergo a humidity-induced phase change that could be well tracked by the fluorescence signal of the surfactant. Taking advantage of the humidity-induced change in fluorescence, the reported ionic DNA complex could accurately indicate the humidity in real time.

DNA-Based Nanomaterials as Drug Delivery Platforms for Increasing the Effect of Drugs in Tumors

DNA nanotechnology has significantly advanced and might be used in biomedical applications, drug delivery, and cancer treatment during the past few decades. DNA nanomaterials are widely used in biomedical research involving biosensing, bioimaging, and drug delivery since they are remarkably addressable and biocompatible. Gradually, modified nucleic acids have begun to be employed to construct multifunctional DNA nanostructures with a variety of architectural designs. Aptamers are single-stranded nucleic acids (both DNAs and RNAs) capable of self-pairing to acquire secondary structure and of specifically binding with the target. Diagnosis and tumor therapy are prospective fields in which aptamers can be applied. Many DNA nanomaterials with three-dimensional structures have been studied as drug delivery systems for different anticancer medications or gene therapy agents. Different chemical alterations can be employed to construct a wide range of modified DNA nanostructures. Chemically altered DNA-based nanomaterials are useful for drug delivery because of their improved stability and inclusion of functional groups. In this work, the most common oligonucleotide nanomaterials were reviewed as modern drug delivery systems in tumor cells.

Programming DNA Tube Circumference by Tile Offset Connection

DNA tubes with prescribed circumferences are appealing for numerous multidisciplinary applications. The DNA single-stranded tiles (SSTs) assembly method has demonstrated an unprecedented capability for programming the circumferences of DNA tubes in a modular fashion. Nevertheless, a distinct set of SSTs is typically required to assemble DNA tube of a specific circumference, with wider tubes requiring higher numbers of tiles of unique sequences, which not only increases the expense and design complexity but also hampers the assembly yield. Herein, we introduce "offset connection" to circumvent such challenges in conventional SST tube assembly. In this new connection scheme, the boundary SST tiles in an SST array are designed to connect in an offset manner. To compensate for the offset, the SST array has to grow wider until the array can close to form a wide tube with a tolerable degree of twist. Using this strategy, we have successfully assembled DNA tubes with prescribed circumferences consisting of 8, 12, 14, 16, 20, 24, 28, 32, 36, 42, 56, or 70 helices from two distinct sets of SSTs composed of 19×4 or 19×14 tiles.

ssDNA-amphiphile architecture used to control dimensions of DNA nanotubes

Controlling the dimensions of DNA nanotubes is of great interest as they can be used in different applications ranging from functional elements in nanodevices to carriers for drug delivery. ssDNA-amphiphiles composed of a ssDNA headgroup, a hydrophobic dialkyl tail and a polycarbon spacer between the tail and the headgroup, self-assemble into hollow DNA nanotubes by forming bilayer nanotapes that transition from twisted nanotapes, to helical nanotapes, to nanotubes. The presence of the DNA nanotubes is verified via cryo-TEM and SAXS. We further explore the effect of the ssDNA secondary structure and tail length on the assembly of the ssDNA-amphiphiles. We demonstrate that the presence of intermolecular G-quadruplexes in the ssDNA sequence dictates the nanotube length. The nanotube diameter is controlled by the hydrophobic tail length, and coarse-grained molecular dynamics simulations are employed to elucidate the tail design impact on assembly.

Photoregulation between small DNAs and reversible photochromic molecules

Oligonucleotides are widely used biological materials in the fields of biomedicine, nanotechnology, and materials science. Due to the demands for the photoregulation of DNA activities, scientists are placing more and more research interest in the interactions between reversible photochromic molecules and DNAs. Photochromic molecules can work as switches for regulating the DNAs' behavior under light irradiation; meanwhile, DNAs also exert influence over the photochromic molecules. The photochromic molecules can be attached to DNAs either by covalent bonds or by noncovalent forces, which results in different regulative functions. Azobenzenes, spiropyrans, diarylethenes, and stilbene-like compounds are important photochromic molecules working as photoswitches. By summarizing their interactions with oligonucleotides, this review intends to facilitate the relevant research on oligonucleotides/photochromic molecules in the biological and medicinal fields and in materials science.

Static DNA Nanostructures For Cancer Theranostics: Recent Progress In Design And Applications

Among the various nano/biomaterials used in cancer treatment, the beauty and benefits of DNA nanocomposites are outstanding. The specificity and programmability of the base pairing of DNA strands, together with their ability to conjugate with different types of functionalities have realized unsurpassed potential for the production of two- and three-dimensional nano-sized structures in any shape, size, surface chemistry and functionality. This review aims to provide an insight into the diversity of static DNA nanodevices, including DNA origami, DNA polyhedra, DNA origami arrays and bioreactors, DNA nanoswitch, DNA nanoflower, hydrogel and dendrimer as young but promising platforms for cancer theranostics. The utility and potential of the individual formats in biomedical science and especially in cancer therapy will be discussed.

Biomimetic DNA Nanotubes: Nanoscale Channel Design and Applications

Biomacromolecular nanotubes play important physiological roles in transmembrane ion/molecule channeling, intracellular transport, and inter-cellular communications. While genetically encoded protein nanotubes are prevalent in vivo, the in vitro construction of biomimetic DNA nanotubes has attracted intense interest with the rise of structural DNA nanotechnology. The abiotic use of DNA assembly provides a powerful bottom-up approach for the rational construction of complex materials with arbitrary size and shape at the nanoscale. More specifically, a typical DNA nanotube can be assembled either with parallel-aligned DNA duplexes or by closing DNA tile lattices. These artificial DNA nanotubes can be tailored and site-specifically modified to realize biomimetic functions including ionic or molecular channeling, bioreactors, drug delivery, and biomolecular sensing. In this Minireview, we aim to summarize recent advances in design strategies, including the characterization and applications of biomimetic DNA nanotubes.

Active, Autonomous, and Adaptive Polymeric Particles for Biomedical Applications

Nature's motors are complex and efficient systems, which are able to respond to many different stimuli present in the cell. Nanomotors for biomedical applications are designed to mimic nature's complexity; however, they usually lack biocompatibility and the ability to adapt to their environment. Polymeric vesicles can overcome these problems due to the soft and flexible nature of polymers. Herein we will highlight the recent progress and the crucial steps needed to fabricate active and adaptive motor systems for their use in biomedical applications and our approach to reach this goal. This includes the formation of active, asymmetric vesicles and the incorporation of a catalyst, together with their potential in biological applications and the challenges still to overcome.

Fabrication of DNA nanotubes with an array of exterior magnetic nanoparticles

Described here a methodology for arraying of magnetic nanoparticles (MNPs) on the surface of DNA nanotubes (DNTs). Positioning of magnetic nanoparticles at exterior surface of DNTs were shaped after self-assembling of oligonucleotide staples within an M13mp18 DNA scaffold via an origami process. The staples were partially labeled with biotin to be arrayed at the surface of DNTs. Gel retardation assay of the DNTs carrying magnetic nanoparticles indicated a reversely behavioral electrophoretic movement in comparison to the nanotubes have been demonstrated previously. Also, high resolution transmission electron microscopy confirmed positioning magnetic nanoparticles at the exterior surface of DNTs, correctly. Ultrastructural characteristics of these DNA nanotubes using atomic force microscopy demonstrated topographic heights on their surfaces formed through positioning of magnetic nanoparticles outside the tubules. This nanoarchitecture would be potential for multiple arraying of nanoparticles that those be useful as functionalized chimeric nanocarriers for developing novel nanodrugs and nanobiosensors.

A Nonconventional Approach to Patterned Nanoarrays of DNA Strands for Template-Assisted Assembly of Polyfluorene Nanowires

DNA molecules have been widely recognized as promising building blocks for constructing functional nanostructures with two main features, that is, self-assembly and rich chemical functionality. The intrinsic feature size of DNA makes it attractive for creating versatile nanostructures. Moreover, the ease of access to tune the surface of DNA by chemical functionalization offers numerous opportunities for many applications. Herein, a simple yet robust strategy is developed to yield the self-assembly of DNA by exploiting controlled evaporative assembly of DNA solution in a unique confined geometry. Intriguingly, depending on the concentration of DNA solution, highly aligned nanostructured fibrillar-like arrays and well-positioned concentric ring-like superstructures composed of DNAs are formed. Subsequently, the ring-like negatively charged DNA superstructures are employed as template to produce conductive organic nanowires on a silicon substrate by complexing with a positively charged conjugated polyelectrolyte poly[9,9-bis(6'-N,N,N-trimethylammoniumhexyl)fluorene dibromide] (PF2) through the strong electrostatic interaction. Finally, a monolithic integration of aligned arrays of DNA-templated PF2 nanowires to yield two DNA/PF2-based devices is demonstrated. It is envisioned that this strategy can be readily extended to pattern other biomolecules and may render a broad range of potential applications from the nucleotide sequence and hybridization as recognition events to transducing elements in chemical sensors.

Self-assembly of DNA nanotubes with defined diameters and lengths

Nanotubes with different sizes can be readily assembled from simple DNA nanomotifs, which consist of just a few unique DNA sequences. Such structurally well-defi ned DNA-nanotubes will have great potential in many technological applications ranging from drug delivery, to determination of biomacromolecular 3D structures, to nanoplasmonic devices.

Topography-controlled alignment of DNA origami nanotubes on nanopatterned surfaces

The controlled positioning of DNA nanostructures on technologically relevant surfaces represents a major goal along the route toward the full-scale integration of DNA-based materials into nanoelectronic and sensor devices. Previous attempts to arrange DNA nanostructures into defined arrays mostly relied on top-down lithographic patterning techniques combined with chemical surface functionalization. Here we combine two bottom-up techniques for nanostructure fabrication, i.e., self-organized nanopattern formation and DNA origami self-assembly, in order to demonstrate the electrostatic self-alignment of DNA nanotubes on topographically patterned silicon surfaces. Self-organized nanoscale ripple patterns with periodicities ranging from 20 nm to 50 nm are fabricated by low-energy ion irradiation and serve as substrates for DNA origami adsorption. Electrostatic interactions with the charged surface oxide during adsorption direct the DNA origami nanotubes to the ripple valleys and align them parallel to the ripples. By optimizing the pattern dimensions and the Debye length of the adsorption buffer, we obtain an alignment yield of ∼70%. Since this novel and versatile approach does not rely on any chemical functionalization of the surface or the DNA nanotubes, it can be applied to virtually any substrate material and any top-down or bottom-up nanopatterning technique. This technique thus may enable the wafer-scale fabrication of ordered arrays of functional DNA-based nanowires.

A polypeptide-DNA hybrid with selective linking capability applied to single molecule nano-mechanical measurements using optical tweezers

Many applications in biosensing, biomaterial engineering and single molecule biophysics require multiple non-covalent linkages between DNA, protein molecules, and surfaces that are specific yet strong. Here, we present a novel method to join proteins and dsDNA molecule at their ends, in an efficient, rapid and specific manner, based on the recently developed linkage between the protein StrepTactin (STN) and the peptide StrepTag II (ST). We introduce a two-step approach, in which we first construct a hybrid between DNA and a tandem of two STs peptides (tST). In a second step, this hybrid is linked to polystyrene bead surfaces and Maltose Binding Protein (MBP) using STN. Furthermore, we show the STN-tST linkage is more stable against forces applied by optical tweezers than the commonly used biotin-Streptavidin (STV) linkage. It can be used in conjunction with Neutravidin (NTV)-biotin linkages to form DNA tethers that can sustain applied forces above 65 pN for tens of minutes in a quarter of the cases. The method is general and can be applied to construct other surface-DNA and protein-DNA hybrids. The reversibility, high mechanical stability and specificity provided by this linking procedure make it highly suitable for single molecule mechanical studies, as well as biosensing and lab on chip applications.

Beyond DNA origami: the unfolding prospects of nucleic acid nanotechnology

Nucleic acid nanotechnology exploits the programmable molecular recognition properties of natural and synthetic nucleic acids to assemble structures with nanometer-scale precision. In 2006, DNA origami transformed the field by providing a versatile platform for self-assembly of arbitrary shapes from one long DNA strand held in place by hundreds of short, site-specific (spatially addressable) DNA 'staples'. This revolutionary approach has led to the creation of a multitude of two-dimensional and three-dimensional scaffolds that form the basis for functional nanodevices. Not limited to nucleic acids, these nanodevices can incorporate other structural and functional materials, such as proteins and nanoparticles, making them broadly useful for current and future applications in emerging fields such as nanomedicine, nanoelectronics, and alternative energy.

Recent advances in DNA-based directed assembly on surfaces

In the last decade, "small" and "integrated" have been keywords in the field of device fabrication as the desire to exploit nanoscale phenomena and make electronic, photonic and magnetic arrays has grown. In an effort to improve resolution and control costs, much work has been dedicated to developing alternatives to conventional microfabrication technology. For this purpose, biomolecular assembly and DNA nanotechnology in particular are appealing owing to their inherent size and capacity for molecular recognition. Herein, we review recent achievements in DNA-based directed assembly on substrates. These include novel methods for patterning and depositing nanomaterials on DNA-modified surfaces as well as using synthetic DNA nanostructures such as DNA tiles and origami as templates to direct the assembly of nanoscale components. Particular attention is paid to integrating self-assembly with top-down lithography, and some possible directions for future work are discussed.

Self-assembly of three-dimensional DNA nanostructures and potential biological applications

A current challenge in nanoscience is to achieve controlled organization in three-dimensions, to provide tools for biophysics, molecular sensors, enzymatic cascades, drug delivery, tissue engineering, and device fabrication. DNA displays some of the most predictable and programmable interactions of any molecule, natural or synthetic. As a result, 3D-DNA nanostructures have emerged as promising tools for biology and materials science. In this review, strategies for 3D-DNA assembly are discussed. DNA cages, nanotubes, dendritic networks, and crystals are formed, with deliberate variation of their size, shape, persistence length, and porosities. They can exhibit dynamic character, allowing their selective switching with external stimuli. They can encapsulate and position materials into arbitrarily designed patterns, and show promise for numerous biological and materials applications.

Fundamental properties of oligo double-stranded DNA/single-walled carbon nanotube nanobiohybrids

Fundamental properties of single-walled carbon nanotubes (SWNTs) that are individually dissolved using twenty base paired-double-stranded (ds) DNA, (dA)(20)/(dT)(20), as well as single-stranded (ss) twenty-mers of oligo DNAs, adenine (dA)(20) and thymine (dT)(20), for comparison are described. In this study, unbound oligo DNAs are fully removed from the hybrid aqueous solutions using size-exclusion chromatography (SEC)-HPLC. Each SEC chromatogram of the solutions shows two separated peaks; one is the free oligo DNAs and the others are the oligo DNA/SWNT hybrids. The earlier eluent fractions (the hybrids) are separated into four size-separated fractions, and then their stability is evaluated by the re-injection of the fractions. The chromatograms of the earlier eluent fractions are almost identical to those of the original ones even after storage for one month, indicating the high stability of the dsDNA/SWNTs and ssDNA/SWNTs hybrids in water. The results free us from considering the desorption of the bound-oligo dsDNA or oligo ssDNA from their nanohybrids with the SWNTs, which is of significant advantage to the utilization of oligo DNA/SWNT nanobiohybrids in wide areas of science. We also investigated the near-IR absorption and photoluminescence (PL) spectral behaviors of the fractionated oligo DNA/SWNTs hybrids not containing corresponding free oligo DNA.

Production of semiconducting gold-DNA nanowires by application of DC bias

There is considerable interest in using DNA nanowires or nanotubes in a wide variety of bioelectronic applications and microcircuitry. Various methods have been developed to construct DNA nanostructures. Here, we report a novel method to construct semiconducting DNA nanowires by applying a suitable DC bias to a gold plating solution containing double-stranded DNA. The self-assembled nanowires fabricated by this method contain attached gold nanoparticles. Further, we report that the dimensions of the nanowires can be easily manipulated by altering the applied DC bias. We also confirmed the semiconducting nature of the DNA nanowires by studying their resistance-temperature behavior from 25 to 65 degrees C in a microelectrode system. These studies describe a simple process by which gold-decorated, semiconducting DNA nanowires could be created and may lead to a breakthrough in the field of self-assembly of nanometer-scale circuits. The self-assembled structures do have some similarity with tube-like structures but in the present work we are using the term 'DNA nanowires' to define the structures.

DNA self-assembly for nanomedicine

Self-assembling DNA nanostructures based on rationally designed DNA branch junction molecules has recently led to the construction of patterned supramolecular structures with increased complexities. An intrinsic value of DNA tiles and patterns lies in their utility as molecular pegboard for deterministic positioning of molecules or particles with accurate distance and architectural control. This review will discuss the state-of-art developments in self-assembled DNA nanostructural system. Biomedical aspects of information guided DNA nanostructures will also be summarized. We illustrate both the use of simple DNA artworks for sensing, computation, drug delivery and the application of more complex DNA architectures as scaffolds for the construction of protein and nanoparticle arrays.

By what means should nanoscaled materials be constructed: molecule, medium, or human?

There is great potential in nanoscale science and technology, and construction of macrosized materials and systems possessing nanoscale structural features is a crucial factor in the everyday application of nanoscience and nanotechnology. Because nanoscale substances are often constructed through self-assembly of unit molecules and nanomaterials, control of the self-assembly process is required. In order to establish general guidelines for the fabrication of materials with nanoscale structural characteristics, i.e., nanoscaled materials, we introduce here examples of recent research in related fields categorised as: (i) self-assembled structures with forms generally determined by intrinsic interactions between molecules and/or unit nanomaterials, (ii) self-assemblies influenced by their surrounding media, especially interfacial environments, (iii) modulation of self-assembly by artificial operation or external stimuli. Examples are not limited to organic molecules, which are often regarded as the archetypal species in self-assembly chemistry, and many examples of inorganic assemblies and hybrid structures are included in this review.

Large-area spatially ordered arrays of gold nanoparticles directed by lithographically confined DNA origami

The development of nanoscale electronic and photonic devices will require a combination of the high throughput of lithographic patterning and the high resolution and chemical precision afforded by self-assembly. However, the incorporation of nanomaterials with dimensions of less than 10 nm into functional devices has been hindered by the disparity between their size and the 100 nm feature sizes that can be routinely generated by lithography. Biomolecules offer a bridge between the two size regimes, with sub-10 nm dimensions, synthetic flexibility and a capability for self-recognition. Here, we report the directed assembly of 5-nm gold particles into large-area, spatially ordered, two-dimensional arrays through the site-selective deposition of mesoscopic DNA origami onto lithographically patterned substrates and the precise binding of gold nanocrystals to each DNA structure. We show organization with registry both within an individual DNA template and between components on neighbouring DNA origami, expanding the generality of this method towards many types of patterns and sizes.

Micrometer-sized DNA-single-fluorophore-DNA supramolecule: synthesis and single-molecule characterization

The synthesis of single-fluorophore-bis(micrometer-sized DNA) triblock supramolecules and the optical and structural characterization of the construct at the single-molecule level is reported. A fluorophore-bis(oligodeoxynucleotide) triblock is synthesized via the amide-coupling reaction. Subsequent protocols of DNA hybridization/ligation are developed to form the supramolecular triblock structure with lambda-DNA fragments on the micrometer length scale. The successful synthesis of the micrometer-sized DNA-single-fluorophore-DNA supramolecule is confirmed by agarose gel electrophoresis with fluorescence imaging under UV excitation. Single triblock structures are directly imaged by combined scanning force microscopy and single-molecule fluorescence microscopy, and provide unambiguous confirmation of the existence of the single fluorophore inserted in the middle of the long DNA. This type of triblock structure is a step closer to providing a scaffold for single-molecule electronic devices after metallization of the DNAs.

Ultrathin cellulose films of tunable nanostructured morphology with a hydrophobic component

In recent years, a wide range of different methods to implant nanosized patterns on surfaces have been developed. Spin coating immiscible binary polymer blends is a straightforward method to prepare micro- and nanostructures on thin films. This study utilizes binary blends to effortlessly prepare stable, surface-functionalized cellulose films. Blends of trimethylsilyl cellulose (TMSC) majority phase and polystyrene (PS) minority phase in toluene were spin coated into an ultrathin film, and TMSC was hydrolyzed to cellulose. The films were characterized and quantified using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, and quartz crystal microbalance (QCM-D). AFM revealed that horizontally phase-separated structures form during spin coating: after the hydrolyzation of TMSC to cellulose, PS protrudes from cellulose as distinct patches. The patches are disk-like structures with a circular radial cross-section and a height of ca. 5-20 nanometers. The smaller the amount of PS in the original spin coating solution, the smaller the PS island dimensions in the films. The results obtained from the XPS measurements support the AFM results. Water contact angle of the PS/cellulose films increases from 61 degrees to 71 degrees when the relative amount of hydrophobic PS is increased from 1:100 to 1:5. Thus by simply varying the ratio of the film components subtly tailored hydrophobic properties can be achieved. The swelling of the films due to exposure to water was studied by QCM-D. The swelling was not affected by the amount of PS in the blend, and at equivalent cellulose content the blends and pure cellulose films exhibited similar swelling characteristics. In addition, the QCM-D evaluation demonstrated that the films are stable over extended periods of time and are suitable for fundamental studies by QCM-D.

Designer DNA nanoarchitectures

Naturally existing biological systems, from the simplest unicellular diatom to the most sophisticated organ such as the human brain, are functional self-assembled architectures. Scientists have long been dreaming about building artificial nanostructures that can mimic such elegance in nature. Structural DNA nanotechnology, which uses DNA as a blueprint and building material to organize matter with nanometer precision, represents an appealing solution to this challenge. On the basis of the knowledge of helical DNA structure and Watson-Crick base pairing rules, scientists have constructed a number of DNA nanoarchitectures with a large variety of geometries, topologies, and periodicities with considerably high yields. Modified by functional groups, those DNA nanostructures can serve as scaffolds to control the positioning of other molecular species, which opens opportunities to study intermolecular synergies, such as protein-protein interactions, as well as to build artificial multicomponent nanomachines. In this review, we summarize the principle of DNA self-assembly, describe the exciting progress of structural DNA nanotechnology in recent years, and discuss the current frontier.

Assembly and melting of DNA nanotubes from single-sequence tiles

DNA melting and renaturation studies are an extremely valuable tool to study the kinetics and thermodynamics of duplex dissociation and reassociation reactions. These are important not only in a biological or biotechnological context, but also for DNA nanotechnology which aims at the construction of molecular materials by DNA self-assembly. We here study experimentally the formation and melting of a DNA nanotube structure, which is composed of many copies of an oligonucleotide containing several palindromic sequences. This is done using temperature-controlled UV absorption measurements correlated with atomic force microscopy, fluorescence microscopy and transmission electron microscopy techniques. In the melting studies, important factors such as DNA strand concentration, hierarchy of assembly and annealing protocol are investigated. Assembly and melting of the nanotubes are shown to proceed via different pathways. Whereas assembly occurs in several hierarchical steps related to the formation of tiles, lattices and tubes, melting of DNA nanotubes appears to occur in a single step. This is proposed to relate to fundamental differences between closed, three-dimensional tube-like structures and open, two-dimensional lattices. DNA melting studies can lead to a better understanding of the many factors that affect the assembly process which will be essential for the assembly of increasingly complex DNA nanostructures.

A conjoined thienopyrrole oligomer formed by using DNA as a molecular guide

A thienopyrrole oligomer conjoined to DNA was prepared by means of a templated synthesis protocol. The oligomer was formed by reaction, initiated with HRP/H2O2, of thieno[3,2-b]pyrrole monomers attached to cytosine bases. The thienopyrrole oligomer was characterized spectroscopically.