Robert L. Letsinger

Directed Assembly of Periodic Materials from Protein and Oligonucleotide-Modified Nanoparticle Building Blocks

DNA hybridization enables the three-dimensional assembly of Au nanoparticles and streptavidin. The high-density DNA-modified Au nanoparticles were stable to nonspecific binding of streptavidin. Structural and melting investigations on the assemblies showed their formation was reversible.

Synthesis and characterization of DNA with ferrocenyl groups attached to their 5′-termini: electrochemical characterization of a redox-active nucleotide monolayer

A novel 5′-ferrocenyl and 3′-thiol modified nucleotide is used to prepare and characterize, for the first time, a redox-active nucleotide monolayer on Au.

Hybridization of Alternating Cationic/Anionic Oligonucleotides to RNA Segments

Abstract It is shown that oligonucleotide analogues containing alternating phosphodiester groups and cationic groups linked to phosphorus through an amidate bond hybridize to complementary RNA segments. An improved synthetic procedure for the alternating compounds is also described.

OLIGONUCLEOTIDES WITH ALTERNATING ANIONIC AND CATIONIC PHOSPHORAMIDATE LINKAGES : SYNTHESIS AND HYBRIDIZATION OF STEREO-UNIFORM ISOMERS

Abstract An oligonucleotide containing alternating anionic and stereo-uniform cationic dimethylaminopropyl-phosphoramidate linkages, d(T+T−) 7 T, is shown to bind with unusually high affinity to DNA [poly(dA) and d(C 2 A 15 C 2 )] and RNA [poly(rA)] targets in solutions of low ionic strength. The isomeric oligomer with the opposite configuration at the phosphoramidate links binds much less efficiently.

A gold nanoparticle/latex microsphere-based colorimetric oligonucleotide detection method*

An exceptionally simple and effective DNA detection methodology based on latex microsphere and gold nanoparticle probes has been developed. The latex and gold particle probes, which were functionalized with separate oligonucleotide sequences, undergo hybridization in the presence of target strands that are complementary to both of the probes. Duplex formation thus results in linking of gold nanoparticles to the latex microspheres and a corresponding white-to-red color change, which, because of the particularly large extinction coefficient of the gold nanoparticles, is clearly visible to the naked eye. Background signal caused by unbound gold nanoparticles is significantly reduced by filtering the solution containing the sample and probes through a size-selective cellulose acetate membrane. The unbound gold probes move freely through this membrane while the larger latex particles are trapped. Therefore, if the latex and gold nanoparticles are joined together via the target oligonucleotides, the membrane appears red, indicating a positive test result. If no hybridization takes place, the membrane appears white, indicating a negative result. The lower detection limits for this system are 500 pM for a 24 base single-stranded target and 2.5 nM for a duplex target oligonucleotide.

Informational liposomes: Complexes derived from cholesteryl-conjugated oligonucleotides and liposomes

Abstract Oligonucleotides with cholesteryl groups tethered near one or both termini bind efficiently to liposomes. Liposomes tagged with such oligonucleotides are recognized by complementary oligonucleotides free in solution or bound to a membrane, as shown by experiments in which the liposomes are precipitated or are immobilized on a membrane as a consequence of hybridization.

A new approach to synthesis of Oligonucleotides with 3′ phosphoryl groups

A convenient method for synthesizing oligonucleotide 3′phosphates utilizes a diester phosphoramidate linker obtained by considering a nucleoside phosphoramidite reagent with an aminoalkyl solid support. Oligomer release is effected by NH3;H+.

Distance-dependent photoinduced electron transfer in synthetic single-strand and hairpin DNA

Abstract The singlet state of stilbene-4,4′-dicarboxamide can serve as a fluorescent probe of both DNA conformation and electron transfer. Covalent incorporation of the stilbene-dicarboxamide into DNA structures with restricted conformational mobility results in inhibition of stilbene isomerization and an increase in its fluorescence quantum yield and lifetime. The fluorescence of stilbenedicarboxamide is selectively quenched by proximate guanine, but not by the three other DNA nucleobases. Selective quenching occurs via an electron transfer mechanism in which stilbene serves as the electron acceptor and guanine as the electron donor. Kinetic analysis of the distance dependence of electron transfer in stilbene-bridged hairpins suggests that duplex DNA is more effective than proteins as a medium for electron transfer, but that it does not function as a molecular wire.

Anchor for one step release of 3′-aminooligonucleotides from a solid support

Abstract A linker is described that permits covalently bound aminooligonucleotides to be liberated from a solid support by one step treatment with ammonium hydroxide.

CHEMICAL AND PHOTOCHEMICAL LIGATION OF OLIGONUCLEOTIDE BLOCKS

Abstract Several efficient means for joining oligonucleotides in dilute solution by non-natural internucleotide bridges are discussed. It is also shown that an oligonucleotide containing a -OP(O)(O−)S- link can hnction as an effective template in PCR amplification and that oligonucleotide probes containing stilbenedicarboxamide groups can serve in monitoring the presence of mismatched bases in an oligonucleotide target.