Design and Synthesis of an Efficient Fluorescent Probe Based on Oxacalix[4]arene for the Selective Detection of Trinitrophenol (TNP) Explosives in Aqueous System

We present the synthesis of a new oxacalix[4]arene system, DMANSOC, wherein two 5-(dimethylamino)-1-naphthalene sulfonamide subunits are attached to the lower rims of the basic oxacalix[4]arene platform. Extensive spectrophotometric studies were conducted to investigate the selectivity and sensitivity of DMANSOC towards nitroaromatic explosives. Detailed analysis of spectrophotometric data, utilizing techniques such as Stern-Volmer, Benesi-Hildebrand, Job's plot, and interference study, unequivocally demonstrated the effectiveness of DMANSOC as a highly efficient fluorescent sensor for 2,4,6-trinitrophenol explosive (TNP) detection in an aqueous medium. The sensor exhibited a linear concentration range of 7.5 μM to 50 μM, with a low detection limit of 4.64 μM and a high binding affinity of 2.45 × 104 M towards TNP. Furthermore, the efficiency of the sensor in environmental samples contaminated with TNP was evaluated, yielding excellent recovery rates. Complementary DFT calculations and molecular dynamics simulations were performed to elucidate the mechanism behind the selective fluorescence quenching of DMANSOC in the presence of TNP.

Handheld UV spectrophotometer device for detection of methamphetamine hydrochloride based on supramolecular sensing platform

The realization of drug detection in drug-using crime sites can provide law enforcement officials with direct evidence. This research has developed and demonstrated an easy-to-use handheld sensor that can quickly detect methamphetamine (MA) in the field. The core of the handheld UV spectrophotometer device (HUVSD) is the STM32F103 series of single-chip micro-controller, which has a 32-bit microcontroller and two embedded 12-bit high-precision analog-to-digital converter (ADC) modules. Through Bluetooth-wireless transmission protocol, the spectral information can be displayed in the cell phone's app, and it is possible to visually determine whether the test sample contains methamphetamine hydrochloride substances based on the characteristic peak at 410 nm. The readily available and inexpensive inducible compound 3A and the phosphate pillar[5]arene@silver nanoparticle (PP5@AgNPs) colloidal solution were used as the reactants. The PP5@AgNPs colloidal solution and 3A were mixed and reacted at room temperature, and the color changed to gray-black. The color change was caused by the aggregation of AgNPs induced by the molecular recognition between the induction compound 3A and PP5 on the AgNPs surface. After continuing to add the drug MA, the color of the colloidal solution turned yellow again. This is due to the occurrence of competitive molecular recognition, and the interaction between PP5 and 3A/MA was investigated by molecular docking simulations. The HUVSD has high sensitivity, simple equipment, time-saving, color change visualization and suitable for on-site deployment. It only needs a Pasteur pipette, which has great potential to realize rapid on-site detection.

Self-Assembled Plasmonic Nanojunctions Mediated by Host-Guest Interaction for Ultrasensitive Dual-Mode Detection of Cholesterol

Herein, a fluorescence and surface-enhanced Raman spectroscopy dual-mode system was designed for cholesterol detection based on self-assembled plasmonic nanojunctions mediated by the competition of rhodamine 6G (R6G) and cholesterol with β-cyclodextrin modified on gold nanoparticles (HS-β-CD@Au). The fluorescence of R6G was quenched by HS-β-CD@Au due to the fluorescence resonance energy transfer effect. When cholesterol was introduced as the competitive guest, R6G in the cavities of HS-β-CD@Au was displaced to recover its fluorescence. Moreover, two of HS-β-CD@Au can be linked by one cholesterol to form a more stable 2:1 complex, and then, plasmonic nanojunctions were generated, which resulted in the increasing SERS signal of R6G. In addition, fluorescence and SERS intensity of R6G increased linearly with the increase in the cholesterol concentrations with the limits of detection of 95 and 74 nM, respectively. Furthermore, the dual-mode strategy can realize the reliable and sensitive detection of cholesterol in the serum with good accuracy, and two sets of data can mutually validate each other, which demonstrated great application prospects in the surveillance of diseases related with cholesterol.

Host–guest sensing towards sodium cyclamate based on a cationic pillar[6]arene reduced graphene nano-composite

A competitive fluorescence sensing for the detection of sodium cyclamate based on a cationic water-soluble pillar[6]arene graphene nano-composite.

Photocatalytic H2 Production from Water by Metal-free Dye-sensitized TiO2 Semiconductors: The Role and Development Process of Organic Sensitizers

The utilization of solar energy to produce hydrogen from water is showing increased importance and desirability in the field of artificial photosynthesis to produce clean and sustainable fuels. In a typical three-component dye-sensitized semiconductor system for photocatalysis, the dye sensitizer plays an essential role of energy antenna for harvesting visible light and promoting the reduction reaction to generate hydrogen. In recent decades, a lot of attention has focused on metal-free organic sensitizers, which have the advantages of low cost, high molar extinction coefficient, good modifiability and, most importantly, ability to avoid the use of noble metal ions. This Review enumerates the design strategies, specific properties and photocatalytic performances of metal-free sensitizers in the past 30 years and concludes their evolution process. The advantages of different types of metal-free sensitizers are highlighted and the instructively enlightening experiences are systematic summarized.

Ultrasensitive electrochemical detection of methyl parathion pesticide based on cationic water-soluble pillar[5]arene and reduced graphene nanocomposite

We report a rapid, sensitive and selective electrochemical sensor based on pillar[5]arene (CP5) reduced graphene (rGO) nanohybrid-modified glassy carbon electrode CP5-rGO/GCE for the trace detection of methyl parathion (MP) by differential pulse voltammetry (DPV) for the first time. Compared to beta-cyclodextrin (β-CD)-functionalized reduced graphene (rGO)-modified GCE β-CD-rGO/GCE, the proposed CP5-rGO/GCE sensor exhibits excellent electrochemical catalytic activity, rapid response, high sensitivity, good reproducibility and anti-interference ability towards MP. The recognition mechanism of β-CD/MP and CP5/MP was studied by ¹H NMR. The results indicate a higher supramolecular recognition capability between CP5 and MP compared to that between β-CD and MP. The β-CD-rGO and CP5-rGO nano-composites were prepared via a wet chemistry approach. The resulting nano-composites have been characterized by thermogravimetric analysis (TGA), fourier transform infrared spectrometry (FTIR), charge transfer resistance (R_ct) and zeta potential. The CP5-rGO/GCE combines the merits of CP5 and rGO, and is used for quantitative detection of MP. It has a low detection limit of 0.0003 μM (S/N = 3) and a linear response range of 0.001–150 μM for MP. This method has been used to detect MP in soil and waste water samples with satisfactory results. This study provides a promising electrochemical sensing platform and is a promising tool for the rapid, facile and sensitive analysis of MP.

A promising electrochemical sensing platform for the detection of methyl parathion based on cationic water-soluble pillar[5]arene reduced graphene nanocomposite.

A Fluorescence Sensing Determination of 2, 4, 6-Trinitrophenol Based on Cationic Water-Soluble Pillar[6]arene Graphene Nanocomposite

We describe a selective and sensitive fluorescence platform for the detection of trinitrophenol (TNP) based on competitive host–guest recognition between pyridine-functionalized pillar[6]arene (PCP6) and a probe (acridine orange, AO) that used PCP6-functionalized reduced graphene (PCP6-rGO) as the receptor. TNP is an electron-deficient and negative molecule, which is captured by PCP6 via electrostatic interactions and π–π interactions. Therefore, a selective and sensitive fluorescence probe for TNP detection is developed. It has a low detection limit of 0.0035 μM (S/N = 3) and a wider linear response of 0.01–5.0 and 5.0–125.0 for TNP. The sensing platform is also used to test TNP in two water and soil samples with satisfying results. This suggests that this approach has potential applications for the determination of TNP.

The synthesis of water-soluble phosphate pillar[5]arenes functionalized graphene as a fluorescent probe for sensitive detection of paraquat

We describe a selective and sensitive fluorescence platform for the detection of paraquat (PQ) based on competitive host-guest recognition between phosphate pillar[5]arenes (PWP5) and probe (Safranine T, ST) with using PWP5 functionalized reduced graphene (PWP5-rGO) as the receptor. PQ is a positive charge molecule that is captured by PWP5 via electrostatic interactions. The host-guest interaction between PWP5 and PQ is studied by ¹H NMR. Therefore, a selective and sensitive fluorescence sensing of detection PQ is developed. It has a linear response ranges of 0.01-2.0 and 2.0-50.0 μM and a low detection limit of 0.0035 μM (S/N = 3) for PQ. The sensing platform is also used to test PQ in two water samples with satisfying results. It suggests that this approach has potential applications for the determination of PQ.

Novel Competitive Fluorescence Sensing Platform for L-carnitine Based on Cationic Pillar[5]Arene Modified Gold Nanoparticles

Supramolecular host-guest interaction and sensing between cationic pillar[5]arenes (CP5) and L-carnitine were developed by the competitive host-guest recognition for the first time. The fluorescence sensing platform was constructed by CP5 functionalized Au nanoparticles (CP5@Au-NPs) as receptor and probe (rhodamine 123, R123), which shown high sensitivity and selectivity for L-carnitine detection. Due to the negative charge and molecular size properties of L-carnitine, it can be highly captured by the CP5 via electrostatic interactions and hydrophobic interactions. The host-guest mechanism between PP5 and L-carnitine was studied by ¹H NMR and molecular docking, indicating that more affinity binding force of CP5 with L-carnitine. Therefore, a selective and sensitive fluorescent method was developed. It has a linear response of 0.1–2.0 and 2.0–25.0 μM and a detection limit of 0.067 μM (S/N = 3). The fluorescent sensing platform was also used to detect L-carnitine in human serum and milk samples, which provided potential applications for the detection of drugs abuse and had path for guarding a serious food safety issues.

A photo-responsive macroscopic switch constructed using a chiral azo-calix[4]arene functionalized silicon surface

A photo-responsive macroscopic switch was fabricated using a chiral azo-calix[4]arene derivative (FC4AD) functionalized silicon surface and exhibited selective and reversible recognition of (1R,2S)-1-amino-2-indanol through the variation of wettability.

Highly-effective palladium nanoclusters supported on para-sulfonated calix[8]arene-functionalized carbon nanohorns for ethylene glycol and glycerol oxidation reactions

Non-Pt noble metal clusters like Pd clusters are considered as promising electrocatalysts for fuel cells, but they suffer from problems such as easy aggregation during the catalysis reactions.

Ultrasensitive electrochemical detection of Dicer1 3'UTR for the fast analysis of alternative cleavage and polyadenylation

Alternative cleavage and polyadenylation (APA) is involved in several important biological processes in animals, e.g. cell growth and development, and cancer progression. The increasing data show that cancer cells are inclined to produce mRNA isoforms with a shortened 3'UTR undergoing APA. For example, the Dicer1 isoform with a shorter 3'untranslated region (3'UTR) was found to be overexpressed in some cancer cells, which may be used as a potential novel prognostic biomarker for cancer. In the present work, a novel electrochemical biosensor for ultrasensitive determination of Dicer1 was designed by using gold nanoparticles and p-sulfonated calix[6]arene functionalized reduced graphene oxide (Au@SCX6-rGO) as nanocarriers. The results showed that the expressions of the shorter 3'UTR (Dicer1-S) both in BT474 and SKBR3 were obviously higher than those of the longer Dicer1 (Dicer1-L) by the constructed biosensor, which agreed well with the result analyzed by the RT-qPCR method. The detection ranges of Dicer1-S and Dicer1-L were 10^-14-10^-9 M and 10^-15-10^-10 M. The LODs were 3.5 and 0.53 fM. The specificity of the proposed biosensor was also very high. For the first time, the expressional analysis of different 3'UTRs caused by APA was studied by an electrochemical method. Moreover, the use of a macrocyclic host for constructing an electrochemical/biosensing platform has rarely been reported. The proposed electrochemical sensing strategy is thus expected to provide a new method for determination of novel biomarkers and a novel method for fast and cheap analysis of APA.

Rapid synthesis of graphene quantum dots using a continuous hydrothermal flow synthesis approach

A rapid and environmentally benign synthesis of green fluorescent graphene quantum dots (GQD) with low cytotoxicity via Continuous Hydrothermal Flow Synthesis (CHFS) aided by calix[4]arene tetrasulfonic acid (SCX4) as a particle size limiting agent.

Synthesis of well-dispersive 2.0 nm Pd–Pt bimetallic nanoclusters supported on β-cyclodextrin functionalized graphene with excellent electrocatalytic activity

Illustration for the preparation of the Pd–Pt@β-CD-RGO nanohybrid using an in situ reduction method.

p-sulfonated calix[8]arene functionalized graphene as a "turn on" fluorescent sensing platform for aconitine determination

This work reports a novel method for the determination of aconitine through the competitive host-guest interaction between p-sulfonated calix[8]arene (SCX8) and signal probe/target molecules by using SCX8 functionalized reduced graphene oxide (SCX8-RGO) as a receptor. Three dyes (ST, RhB, BRB) and aconitine were selected as the probe and target molecules, respectively. The formation of SCX8-RGO·ST, SCX8-RGO·RhB, and SCX8-RGO·BRB complexes greatly decreases the fluorescence emission of ST, RhB, and BRB. The aconitine/SCX8 complex possesses a higher binding constant than ST/SCX8, RhB/SCX8, and BRB/SCX8 complexes, thus the dye in the SCX8 cavity can be replaced by aconitine to revert the fluorescence emission of SCX8-RGO·dye, leading to a "switch-on" fluorescence response. The fluorescence intensity of SCX8-RGO·ST, SCX8-RGO·RhB, and SCX8-RGO·BRB complexes increased linearly with increasing concentration of aconitine ranging from 1.0 to 14.0μM, 2.0-16.0μM, and 1.0-16.0μM, respectively. Based on the competitive host-guest interaction, the proposed detection method for aconitine showed detection limits of 0.28μM, 0.60μM, and 0.37μM, respectively, and was successfully applied for the determination of aconitine in human serum samples with good recoveries from 95.1% to 104.8%. The proposed method showed high selectivity for aconitine beyond competitive binding analytes. In addition, the inclusion complex of the SCX8/aconitine was studied by the molecular docking and molecular dynamics simulation, which indicated that the phenyl ester group of the aconitine molecule was included into the SCX8 cavity.

Indicator displacement assay for cholesterol electrochemical sensing using a calix[6]arene functionalized graphene-modified electrode

Indicator displacement assay for cholesterol (Cho) sensing using CX6–Gra against MB.

A FRET-based fluorescent approach for labetalol sensing using calix[6]arene functionalized MnO2@graphene as a receptor

A turn-on fluorescent sensing platform for labetalol has been developed based on competitive host–guest interaction between p-sulfonated calix[6]arene (SCX6) and target molecule by using SCX6 functionalized MnO₂@reduced graphene oxide as a receptor.

Selective molecular recognition on calixarene-functionalized 3D surfaces

Calixarene based various 3D surface materials with unique signal amplification in molecular recognition are presented, including quantum dots (QDs), metal nanoparticles (NPs), nanotubes, and mesoporous silica.

Macroscopic switches constructed through host–guest chemistry

In this feature article, we discuss recent developments in macroscopic contact angle switches formed by different macrocyclic hosts and highlight the properties of these new functional surfaces and their potential applications.

Applications of graphene and its derivatives in intracellular biosensing and bioimaging

Graphene has a unique planar structure, as well as excellent electronic properties, and has attracted a great deal of interest from scientists.

Synthesis of a thiacalix[4]arenetetrasulfonate-functionalized reduced graphene oxide adsorbent for the removal of lead(ii) and cadmium(ii) from aqueous solutions

A thiacalix[4]arenetetrasulfonate-functionalized reduced graphene oxide (TCAS–rGO) adsorbent was synthesized and used as an adsorbent for the removal of lead(ii) and cadmium(ii) from aqueous solutions.

Fluorescent Detection of Tadalafil Based on Competitive Host-Guest Interaction Using p-Sulfonated Calix[6]arene Functionalized Graphene

A competitive fluorescence method toward tadalafil detection has been developed based on host-guest recognition by selecting rhodamine B (RhB) and p-sulfonated calix[6]arene functionalized graphene (CX6-Gra) as the "reporter pair". Upon the presence of tadalafil to the performed CX6-Gra-RhB complex, the RhB molecules are displaced by tadalafil, leading to a "switch-on" fluorescence signal. The observed fluorescence signal can be used for quantitative detection of tadalafil ranging from 1.00 to 50.00 μM with a detection limit of 0.32 μM (S/N = 3). The inclusion complex of tadalafil and CX6 was studied by molecular docking and the results indicated that a 1:1 host-guest stoichiometry had the lowest ΔG value of -7.18 kcal/mol. The docking studies demonstrated that the main forces including π-π interactions, electrostatic interactions, and hydrophobic interactions should be responsible for the formation of this inclusion compound. The mechanism of the competitive host-guest interaction was clarified. The binding constant (K) of the tadalafil/CX6 complex was more than 5 times greater than that of RhB/CX6.

Electrochemical detection of cholesterol based on competitive host–guest recognition using a β-cyclodextrin/poly(N-acetylaniline)/graphene-modified electrode

Illustration of the strategy of the proposed electrochemical sensor based on the competitive host–guest interaction between β-CD and MB (signal probe)/cholesterol (target).

Calix[4]arene triazole-linked pyrene: click synthesis, assembly on graphene oxide, and highly sensitive carbaryl sensing in serum

Graphene oxide modified with a fluorescent calix[4]arene showed a highly selective recognition for carbaryl.

Design and fabrication of a biomimetic nanochannel for highly sensitive arginine response in serum samples

Inspired from their biological counterparts, chemical modification of the interior surface of nanochannels with functional molecules may provide a highly efficient means to control ionic or molecular transport through nanochannels. Herein, we have designed and prepared a aldehyde calix[4]arene (C4AH), which was attached to the interior surface of a single nanochannel by using a click reaction, and that showed a high response for arginine (Arg). Furthermore, the nanofluidic sensing system has been challenged with complex matrices containing a high concentration of interfering sequences and serum. Based on this finding, we believe that the artificial nanochannel can be used for practical Arg-sensing devices, and be applied in a biological environment.

Calix[4,6,8]arenesulfonates functionalized reduced graphene oxide with high supramolecular recognition capability: fabrication and application for enhanced host-guest electrochemical recognition

Reduced graphene oxide (rGO) modified with three kinds of water-soluble p-sulfonated calix[4,6,8]arene sodium (SCn: SC4, SC6, SC8) were successfully prepared by using a simple wet chemical strategy. Three obtained SCn-rGO nanocomposites were characterized by Fourier transform infrared spectroscopy, Ultraviolet-visible spectroscopy, static contact angle measurement, thermogravimetric analysis, scanning electron microscope and electrochemical impedance spectroscopy, which confirmed that different amount of SCn molecules had been effectively loaded onto the surface of rGO, and the water-dispersity and stability of SCn-rGO increased with the increase of the value of n in SCn (n = 4, 6, 8). More significantly, cyclic voltammetry measurement showed that the SCn-rGO could exhibit high supramolecular recognition and enrichment capability and consequently displayed excellent electrochemical response toward four probe molecules (biological and organic dye molecules). Especially, SC8-rGO exhibited an excellent electrochemical performance for dopamine with high current densities of 73.04 mA mM(-1) L cm(-2), broad linear range (1 × 10(-8) to 2.1 × 10(-5) M) and very low detection limit (8 × 10(-9) M) at a signal-to-noise ratio of 3.

Bipyrene-functionalized graphene as a "turn-on" fluorescence sensor for manganese(II) ions in living cells

1,2-bis-(2-pyren-1-ylmethylamino-ethoxy) ethane (NPEY) was synthesized and brought to the surface of graphene nanosheets (GNs) via π-π stacking, which provided a simple and convenient route for processing "turn-on" fluorescent sensor by simply mixing the diluted aqueous solutions of both components. The synthesized NPEY modified graphene nanosheets (NPEY-GNs) not only allows good selectivity toward Mn(2+) with the detection limit of 4.6 × 10(-5) M, but also shows "turn-on" response for Mn(2+) both in vitro and in living cells. These sensing capabilities of NPEY-GNs in living cells make it a robust candidate for many biological fields, such as intracellular tracking, intracellular imaging, etc.