Pillar[n]arene-Based Fluorescence Turn-On Chemosensors for the Detection of Spermine, Spermidine, and Cadaverine in Saline Media and Biofluids

Polyamines are essential analytes due to their critical role in various biological processes and human health in general. Due to their role as regulators for cell growth and proliferation (putrescine and spermine), as neuroprotectors, gero-, and cardiovascular protectors (spermidine), and as bacterial growth indicators (cadaverine), rapid, simple, and cost-effective methods for polyamine detection in biofluids are in demand. The present study focuses on the development and investigation of self-assembled and fluorescent host⋅dye chemo-sensors based on sulfonated pillar[5]arene for the specific detection of polyamines. Binding studies, as well as stability and functionality assessments of the turn-on chemosensors for selective polyamine detection in saline and biologically relevant media, are shown. Furthermore, the practical applicability of the developed chemo-sensors is demonstrated in biofluids such as human urine and saliva.

DNA Chimeras as Electrochemical Biosensors for Host-Guest Measurements in Blood

Few sensing platforms have become ubiquitous to enable rapid and convenient measurements at the point-of-care. Those, however, are "one-off" technologies, meaning that they can only detect a single target and are hardly adaptable. In response, we plan to develop a sensing platform that can be extended to detect other classes of molecules and that affords rapid, convenient, continuous measurements directly in undiluted complex matrices. For this, we decided to rely on a host molecule that presents reversible interactions toward specific guest molecules to develop a new class of sensors that we coined "Electrochemical DNA-host chimeras". As a proof-of-concept for our sensor, we decided to use cyclobis(paraquat-p-phenylene) ("blue box") that we attached on an electrode-bound DNA to allow measurements of electron-rich guests such as dopamine and aspirin. Doing so allows to promote host-guest complex that could be quantified using blue box's electrochemistry. Because of this unique sensor architecture, we achieve, to our knowledge, the first reagentless, continuous and rapid (<5 min) host-guest measurements in undiluted whole blood. We envision that given the library of electroactive host molecules that this will allow the development of a sensing platform for measurements of several classes of molecules in complex matrices at the point-of-care.

Determination of urinary spermine using controlled dissolution of polysulfide modified gold electrode

Spermine (SPM) is considered a biomarker for prostate cancer and detecting it becomes highly challenging due to its electro- and optical-inactive nature. SPM has a tendency to interact with groups such as phosphates and sulfides to form macrocyclic arrangements known as nuclear aggregates of polyamines. Using this tendency, an electrochemical sensor has been developed using a polysulfide (PS) modified Au electrode (PS@Au electrode). PS has been synthesized from elemental sulfur by hydrothermal method and characterized using UV-Vis, fluorescence, FTIR, SEM, and XPS analyses. The PS@Au electrode was employed for electrochemical sensing of SPM. In the presence of SPM, a decrease in gold oxide reduction current was noted which is proportional to the concentration of SPM. The decrease in gold oxide reduction (0.5 V) current was attributed to the complexing nature of SPM-PS at the electrode interface. The reason for the decrease in current has been substantiated using XRF, XPS, and spectroelectrochemical studies. Under the optimized conditions, the PS@Au electrode exhibited a linear range of 1.55-250 µM with LOD of 0.511 ± 0.02 µM (3σ). The electrochemical strategy for SPM sensing exhibited better selectivity even in the presence of possible interferents. The selectivity stems from the selective interaction of SPM with PS on the Au electrode surface; the tested amino acids, and other molecules do not complex with PS and hence they could not interfere. The PS@Au electrode has been subjected to the determination of SPM in artificial urine samples and exhibited outstanding performance in the synthetic sample.

A combination of a graphene quantum dots-cationic red dye donor-acceptor pair and cucurbit[7]uril as a supramolecular sensor for ultrasensitive detection of cancer biomarkers spermine and spermidine

In a unique approach, the combination of a donor-acceptor pair of hydroxy graphene quantum dots (GQDs-OH) and a red-emissive donor-two-acceptor (D-2-A) type dye with pyridinium units (BPBP) and the well-known host cucurbit[7]uril (CB[7]) has been exploited as a supramolecular sensing assembly for the detection of cancer biomarkers spermine and spermidine in aqueous media at the sub-ppb level based on the affinity-driven exchange of guests from the CB[7] portal. In the binary conjugate, green fluorescent GQDs-OH transfers energy to trigger the emission of the dye BPBP and itself remains in the turn-off state. CB[7] withdraws the dye from the surface of GQDs-OH by strong host-guest interactions with its portal, making GQDs-OH fluoresce again to produce a ratiometric response. In the presence of spermine (SP) or spermidine (SPD), their strong affinity with CB[7] forces the ejection of the fluorophore to settle on the GQDs-OH surface, and the strong green emission of GQDs-OH turns off to device a supramolecular sensor for the detection of SP/SPD. The DFT studies revealed interesting excited-state charge-transfer conjugate formation between BPBP and GQDs leading to turn-on emission of the dye, and further supported the stronger binding modes of BPBP-CB[7], indicating the retrieval of the emission of GQDs. The assembly-disassembly based sensing mechanism was also established by Job's plot analysis, particle size analysis, zeta potential, time-resolved spectroscopy, ITC studies, microscopic studies, etc. The supramolecular sensing assembly is highly selective to SP and SPD, and showed nominal interference from other biogenic amines, amino acids, various metal ions, and anions. The limits of detection (LODs) were 0.1 ppb and 0.9 ppb for spermine and spermidine, respectively. The potential for the real-world application of this sensing assembly was demonstrated by spiking SP and SPD in human urine and blood serum with a high %recovery.

A new 5-bromoindolehydrazone anchored diiodosalicylaldehyde derivative as efficient fluoro and chromophore for selective and sensitive detection of tryptamine and F- ions: Applications in live cell imaging

A novel indole hydrazone tagged moiety, 2-((5-bromo-1H-indol-2-yl) methylene) hydrazono) methyl)-4, 6-diiodophenol (BHDL) has been developed for the selective and sensitive detection of biogenic tryptamine and F^- ions. The binding dexterity of probe BHDL towards F^-/tryptamine (TryptA) has been investigated by UV-visible/fluorescence spectroscopy. In the presence of TryptA, probe exhibits strong enhancement in the emission band at 433 nm and the band at 555 nm underwent a blue shift accompanied by a decrease in intensity by the inhibition of Excited State Intramolecular Proton Transfer (ESIPT) on BHDL. Excitingly, complexation with F^- ions as well triggers an enhancement in a fluorescence band at 430 nm with the concomitant disappearance of the emission band at 555 nm due to the inhibition of ESIPT and deprotonation process initiated by the hydrogen bonding complex formation. Further, Density Functional Theoretical (DFT) calculations have been performed to support the mechanism functioned on the probe BHDL in the presence of TryptA/F^-.

Pillar[5]arene-Based Dual Chiral Organoboranes with Allowed Host-Guest Chemistry and Circularly Polarized Luminescence

We first describe two examples of highly luminescent organoboranes (NP5BN1 and NP5BN2) with dual chirality that were achieved by molecular functionalization of planar chiral pillar[5]arenes with naphthyls. Sufficiently strong steric effects are imposed by triarylamine (Ar₃N) and triarylborane (Ar₃B) moieties and further enhanced by the proximity of the chiral building blocks, leading to the isolation of multiple enantiomers via chiral high-performance liquid chromatography. The intramolecular charge transfer from N-donor to B-acceptor across both chiral subunits enabled the circularly polarized luminescence and thermally robust colorimetric responses in their emissions. Furthermore, their remarkable host-guest chemistry was allowed at no expense in the pursuit of advanced chiroptical properties using pillar[5]arene-based supramolecular scaffolds.

A hybrid upconversion nanoprobe for ratiometric detection of aliphatic biogenic amines in aqueous medium

We fabricated an inorganic-organic hybrid upconversion nanoprobe for the ratiometric detection of aliphatic biogenic amines in water. The hybrid nanoprobe comprises a thiophene-based acceptor-π-donor-π-acceptor organic fluorescent dye, TDPM, and near-infrared light-absorbing upconversion nanoparticles (UCNPs). The organic dye was loaded into a mesoporous silica-coated UCNP (UCNP@mSiO2) matrix to circumvent the issues of water insolubility and higher energy excitation. Yb3+ and Tm3+-doped UCNPs exhibited dual emission bands at 475 and 645 nm upon excitation with a 980 nm laser. The significant spectral overlap between the absorption and the emission bands of TDPM and UCNPs, respectively, at 475 nm led to resonance energy transfer (RET) from the UCNPs to TDPM resulting in the quenching of the UCNP emission. In contrast, 'turn-on' emission was noticeable with the addition of aliphatic biogenic amines due to an inhibition of the RET. The emission at 645 nm remained unaffected during the energy transfer process making the hybrid probe a versatile platform for the ratiometric detection of different aliphatic biogenic amines. Furthermore, we explored the sensing of aliphatic biogenic amines in adulterated milk and rotten fish. The unique material attributes demonstrated in the current study hold promise for further development of real-time sensors and switches based on hybrid upconversion nanoprobes.

Pillararene-based self-assemblies for electrochemical biosensors

The ingenious design and synthesis of novel macrocycles bring out renewed vigor of supramolecular chemistry in the past decade. As an intriguing class of macrocycles, pillararene and pillararene-based functional materials that are constructed through the noncovalent bond self-assembly approach have been undergoing a rapid growth, benefiting from their unique structures and physiochemical properties. This review elaborates recent significant advances of electrochemical studies based on pillararene systems. Fundamental electrochemical behavior of pillar[n]arene[m]quinone and pillararene-based self-assemblies as well as their applications in electrochemical biosensors are highlighted. In addition, the advantages and functions of pillararene self-assembly systems resulted from the unique molecular architectures are analyzed. Finally, current challenges and future development tendency in this burgeoning field are discussed from the viewpoint of both fundamental research and applications. Overall, this review not only manifests the main development vein of pillararene-based electrochemical systems, but also conquers a solid foundation for their further bioelectrochemical applications.

Supramolecular kinetic effects by pillararenes: the synergism between spatiotemporal and preorganization concepts in decarboxylation reactions

Spatiotemporal and preorganization factors were both responsible for the catalytic and inhibitory supramolecular effects in decarboxylation reactions.

Towards new nanoporous biomaterials: self-assembly of sulfopillar[5]arenes with vitamin D3 into supramolecular polymers

Novel water-soluble, deca-substituted pillar[5]arenes containing thiasulfate and thiacarboxylate fragments were synthesized and characterized. UV-vis, 2D 1H-1H NOESY and DOSY NMR spectroscopy revealed the ability of pillar[5]arenes containing thiasulfate fragments to form an inclusion complex with cholecalciferol (vitamin D3) in a 1 : 2 ratio (lg Kass = 2.2). Using DLS and SEM it was found that upon concentration and/or evaporation of the solvent, the supramolecular polymer (pillar[5]arene/vitamin D3 (1 : 2)) forms a porous material with an average wall diameter of 53 nm. It was shown that the supramolecular polymer is stable during photolysis by UV radiation (k1 = 1.7 × 10-5 s-1).

Supramolecular neuromuscular blocker inhibition by a pillar[5]arene through aqueous inclusion of rocuronium bromide

A water-soluble pillar[5]arene, decafunctionalized with thioether and carboxylate fragments, was synthesized as a structural analogue of Sugammadex. Its ability to restore the contraction of the diaphragm muscle by encapsulating the muscle relaxant rocuronium bromide was demonstrated. Using UV-vis, NMR and fluorescence spectroscopy, it was shown that the muscle relaxant is associated with the pillar[5]arene with an association constant of 4500 M-1 and a stoichiometry of 1 : 1. The structure of the inclusion complex of the pillar[5]arene with rocuronium bromide was additionally investigated by quantum chemical methods.

Diastereoselective Synthesis of a Dyn[3]arene with Distinct Binding Behaviors toward Linear Biogenic Polyamines

The extension of the family of dyn[ n]arenes toward a three-membered macrocycle is reported. Through a templated approach, a single diastereoisomer of a dyn[3]arene that bears six carboxyl groups could be isolated by precipitation in 59-63% yield and excellent purity (≥95%). A combination of experimental and computational experiments in water at physiological pH revealed that the macrocycle could bind parent biogenic polyamines with a unique diversity of surface-binding modes. Whereas no binding event could be accurately measured with 1,3-diaminopropane, spermidine formed a classical stoichiometric complex with the dyn[3]arene in the millimolar concentration range. On the other hand, the data obtained for spermine could only be attributed to a more complex binding event with the formation of a 2:1 complex at high [host]/[guest] ratios and redistribution toward a 1:1 complex upon further addition of guest.

A Rotaxane Scaffold Bearing Multiple Redox Centers: Synthesis, Surface Modification and Electrochemical Properties

A rotaxane scaffold incorporating two dithiolane anchoring units for the modification of gold surfaces has been functionalized with multiple copies of a redox unit, namely ferrocene. Surface modification has been first assessed at the single molecule level by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) imaging, while tip enhanced Raman spectroscopy (TERS) provided the local vibrational signature of the ferrocenyl subunits of the rotaxanes grafted onto the gold surface. Finally, oxidation of the redox moieties within a rotaxane scaffold grafted onto gold microelectrodes has been investigated by ultrafast cyclic voltammetry. Intramolecular electron hopping is indeed extremely fast in this system. Moreover, the kinetics of charge injection depends on the molecular coverage due to the influence of intermolecular contacts on molecular motions.

Hybrid multicyclophanes based on thiacalix[4]arene and pillar[5]arene: synthesis and influence on the formation of polyaniline

A series of new tetrakispillar[5]thiacalix[4]arenes was synthesized. Supramolecular assistance of the multicyclophanes in oxidative polymerization of aniline was studied.

Recognition and optical sensing of amines by a quartz-bound 7-chloro-4-quinolylazopillar[5]arene monolayer

Pillar[5]arene-decorated quartz slides for the direct detection of linear amines and diamines are now available.