Soft matter pH sensing: from luminescent lanthanide pH switches in solution to sensing in hydrogels

The synthesis, complexation, and photophysical properties of the Eu(III)-based quinoline cyclen conjugate complex Eu1 and its permanent, noncovalent incorporation into hydrogels as sensitive, interference-free pH sensing materials for biological media are described. The Eu(III) emission in both solution and hydrogel media was switched reversibly on-off as a function of pH with a large, greater than order of magnitude enhancement in Eu(III) emission. The irreversible incorporation of Eu1 into water-permeable hydrogels was achieved using poly[methyl methacrylate-co-2-hydroxyethyl methacrylate]- based hydrogels, and the luminescent properties of the novel sensor materials, using confocal laser- scanning microscopy and steady state luminescence, were characterized and demonstrated to be retained with respect to solution behavior. Water uptake and dehydration behavior of the sensor-incorporated materials was also characterized and shown to be dependent on the material composition.

Solid-bound, proton-driven, fluorescent ‘off–on–off’ switches based on PET (photoinduced electron transfer)

Anthracene-based, H+-driven, ‘off–on–off’ fluorescent PET (photoinduced electron transfer) switches are immobilized on organic and inorganic polymeric solids in the form of Tentagel® and silica, respectively. The environment of the organic bead displaces apparent switching thresholds towards lower pH values whereas the Si–O- groups of silica electrostatically cause the opposite effect. These switches are ternary logic gate tags, one of which can be particularly useful in strengthening molecular computational identification (MCID) of small solid objects.

CMOS compatible RF MEMS switches with serpentine springs

This paper describes a serpentine flexure spring design and fabrication process development for radio frequency microelectromechanical (RF MEMS) capacitive switches with coplanar waveguide (CPW) lines. Sputtered tungsten is employed as the CPW line conductor instead of Au, a non-Si compatible material. The bridge membrane is fabricated from Al. The materials and fabrication process can be integrated with CMOS and SOI technology to reduce cost. Results show the MEMS switch has excellent performance with insertion loss 0.3dB, return loss -27dB at 30GHz and high isolation -30dB at 40GHz. The process developed promises to simplify the design and fabrication of RF MEMS on silicon.

40-70 GHz 13 Gbps 1-dB loss SPST and SPDT differential switches in 0.35 μm SiGe technology

This paper presents the design and characterization of ultrafast wideband low-loss single-pole single-throw (SPST) and single-pole double-throw (SPDT) differential switches. The SPDT switch exhibits insertion loss of lower than 1.25 dB from 42 to 70 GHz and isolation of better than 20 dB from 40 to 65 GHz. Similar low-loss and broadband characteristics are also observed from the measured SPST switch. The proposed switch topologies adopting current-steering technique and implemented in 0.35 µm SiGe bipolar technology result in a switching time of only 75 ps. This suggests a maximum switching speed of 13 Gbps, the fastest ever reported at V-band.

Fluorescent switches with high selectivity towards sodium ions:Correlation of ion-induced conformation switching with fluorescence function

Diazacoronand 2 undergoes drastic conformational switching upon binding sodium ions as demonstrated by solution- and solid-state studies, which permit the design of efficient fluorescent PET (photoinduced electron transfer) switches 3a,b.

Modification of Fluorescent Photoinduced Electron Transfer (PET) Sensors/Switches To Produce Molecular Photo-Ionic Triode Action

The fluorophore-spacer₁-receptor₁-spacer₂-receptor₂ system (where receptor₂ alone is photoredox-inactive) shows ionically tunable proton-induced fluorescence off-on switching, which is reminiscent of thermionic triode behavior. This also represents a new extension to modular switch systems based on photoinduced electron transfer (PET) towards the emulation of analogue electronic devices.

Current Developments in Fluorescent PET (Photoinduced Electron Transfer) Sensors and Switches

Following a brief introduction to the principle of fluorescent PET (photoinduced electron transfer) sensors and switches, the outputs of laboratories in various countries from the past year or two are categorized and critically discussed. Emphasis is placed on the molecular design and the experimental outcomes in terms of target-induced fluorescence enhancements and input/output wavelengths. The handling of single targets takes up a major fraction of the review, but the extension to multiple targets is also illustrated. Conceptually new channels of investigation are opened up by the latter approach, e.g. ‘lab-on-a-molecule’ systems and molecular keypad locks. The growing trends of theoretically-fortified design and intracellular application are pointed out.

Oligo switches: photoresponsive oligonucleotide conjugates by solid-supported click chemistry

Photoresponsive oligonucleotides (ONs) incorporating isoxazole-linked azobenzene (AB) moieties were prepared by resin-supported nitrile oxide-alkyne cycloaddition (NOAC) chemistry. The thermal and photochromic properties of the modified ONs were significantly influenced by the extent of pi-conjugation between the isoxazole and the AB modules.

Direct Visual Indication of pH Windows: 'Off-On-Off' Fluorescent PET (Photoinduced Electron Transfer) Sensors/Switches

1–3, which contain a fluorophore and two proton receptors with opposite PET (photoinduced electron transfer) characteristics, only display strong fluorescence within a pH window whose position and width are tunable.

Sensitized terbium(iii) macrocyclic-phthalimide complexes as luminescent pH switches

Four new macrocyclic-phthalimide ligands were synthesised via the coupling of N-(3-bromopropyl)phthalimide either to cyclen (1,4,7,10- tetraazacyclododecane) itself or its carboxylate-functionalized analogues, and photophysical studies were carried out on their corresponding Tb(iii) complexes in aqueous media as a function of pH. Luminescence intensities of Tb·L^1a-Tb·L^3a were in 'switched off' mode under acidic conditions (pH < 4), and were activated on progression to basic conditions as the phthalimido functions therein were hydrolysed to their corresponding phthalamates Tb·L^1b-Tb·L^3b. Emission of phthalamate-based macrocyclic Tb(iii) complexes Tb·L ^1b-Tb·L^3b was in 'switched on' mode between pH 4 and 11, exhibiting high quantum yields (Φ) and long lifetimes (τ) of the order of milliseconds at pH ∼ 6. Tb(iii) emissions were found to decline with increasing number of chromophores. The values of Φ and τ were 46% and 2.4 ms respectively for Tb·L^1b at pH ∼ 6 when activated. This is the best pH-dependent sensor based on a Tb(iii) complex reported to date, benefiting from the macrocyclic architecture of the ligand. © 2013 The Royal Society of Chemistry.