Fluorescence red-shift of gold-silver nanoclusters upon interaction with cysteine and its application

One-Pot facile synthesis of fluorescent copper nanoclusters for highly selective and sensitive detection of tetracycline

Due to the excellent characteristics, fluorescent copper nanoclusters (Cu NCs) have aroused great interest in recent years. Herein, the simple prepared, environmentally friendly fluorescent Cu NCs were synthesized by using trypsin as the stabilizer and applied for the determination of tetracycline. Uniformly dispersed Try-Cu NCs were obtained with average size of 3.5 ± 0.3 nm and some excellent merits of good water solubility, UV light stability and salt stability. Emission peaks around 460.0 nm were visibly quenched by tetracycline based on static quenching mechanism and inner filter effect (IFE). Two excellent linear relationships were observed between ln(F0/F) and tetracycline concentrations in the range of 1-100 μM and 100-300 μM with limit of detection (LOD) of 0.084 μM. Meanwhile, this nanoprobe exhibited an apparent selectivity for tetracycline detection. Moreover, Try-Cu NCs were successfully employed to determine tetracycline in serum and milk samples after facile pretreatment with satisfactory recovery rates and credible standard deviation. The results suggested that this as-prepared Try-Cu NCs had excellent application prospects in the future.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 μM with a detection limit of 0.092 μΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

Nanoclusters with specific DNA overhangs: modifying configurability, engineering contrary logic pairs and the parity generator/checker for error detection

The most promising alternative for next-generation molecular computers is biocomputing, which uses DNAs as its primary building blocks to perform a Boolean operation. DNA nanoclusters (NCs) have emerged as promising candidates for biosensing applications due to their unique self-assembly properties and programmability. It has been demonstrated that adding DNA overhangs to DNA NCs improves their adaptability in identifying specific biomolecular interactions. A recent proposal in DNA computing is the concept of "contrary logic pairs (CLPs)" executed by employing a DNA hybrid architecture as a universal platform. We have designed thymine overhang-modified DNA-templated NCs (T-Au/Ag NCs). These NCs serve as a chemosensing ensemble platform, where the presence of HgII ions mediates the formation of M-Au/Ag NCs. The resulting NCs exhibit the capability to drive elementary CLPs (YES, NOT, OR, NOR, INH and IMP) as well as complex logic operations (XOR and XNOR). Additionally, they can be utilized for advanced non-arithmetic DNA logic devices like a parity generator (pG) and a parity checker (pC) for "error detection". Bit errors are an unavoidable and common occurrence during any computing. A cascade of XOR operations was used to evaluate these errors by introducing the pG and pC at the transmitting (TX) and receiving (RX) ends in binary transmission, respectively, which has devastating implications for reliable logic circuits, especially in advanced logic computation. Moreover, an even/odd natural number from 0 to 9 distinguishable pC was designed based on a dual-source responsive computing platform. This work offers inspiring avenues for a cost-effective strategy to construct highly-intelligent DNA computing devices by enhancing the multi-input responsive single DNA platform concept.

Inner filter effect-based red-shift and fluorescence dual-sensor platforms with sulfur quantum dots for detection and bioimaging of alkaline phosphatase

Alkaline phosphatase (ALP), one of the vital biomarkers in several diseases, plays a role in indicating disease presence or severity in early diagnosis. Here, a simple H₂O₂ assisted top-down method was used to synthesize sulfur quantum dots (SQDs) with excitation and emission at 355 nm and 440 nm. Adding ALP into p-nitrophenyl phosphate (p-NPP) and SQDs was found to exhibit a red shift in the emission wavelength and fluorescence intensity quenching of SQDs, respectively, allowing us to propose dual-sensor platforms of red shift of emission wavelength (RSEW) and fluorescence quenching of SQDs. These dual-sensor platforms were highly sensitive and selective in ALP detection, with a linear response to ALP in the concentration range of 0.25 to 100 U L^-1 and detection limits of 0.08 and 0.10 U L^-1, respectively. The absorption of p-NP at 400 nm showed a good overlap with the excitation and emission of SQDs, leading to inner filter effect-based RSEW and fluorescence quenching of SQDs. This sensor platform was successfully applied in ALP sensing of serum samples as well as monitoring of ALP in cells. More importantly, this platform can serve as an example of using RSEW to detect ALP.

A self-healing carboxymethyl chitosan/oxidized carboxymethyl cellulose hydrogel with fluorescent bioprobes for glucose detection

Self-healing hydrogel as a soft material with high durability and life-time has been successfully applied in various fields, including electronic skins, wearable electronic devices, and soft sensors. However, it is still a challenge to design a hydrogel with rapid self-healing, biodegradable and biosensing properties. Here, a self-healing carboxymethyl chitosan (CMCS)/oxidized carboxymethyl cellulose (OCMC) hydrogel with fluorescent bioprobes was developed for glucose detection. In this biosensing system, gold nanoclusters (AuNCs) and glucose oxidase (GOx) were encapsulated into the CMCS/OCMC hydrogel matrix as the fluorescent bioprobes. The CMCS/OCMC hydrogel with fluorescent bioprobes exhibited high sensitivity for glucose sensing with a linearly detection range of 100 μM to 5 mM and a detection limit of 0.029 mM, which covered the level of glucose in clinical detection. Furthermore, this hydrogel exhibited good biocompatibility. Finally, In vitro blood fluorescence tests and in vivo fluorescence investigation of the AuNCs-CMCS/OCMC hydrogel in diabetic mice indicated that this biocompatible and self-healing hydrogel based on fluorescent sensing system had potential application in implantable biosensing area for glucose monitoring.

Novel luteolin sensor of tannic acid-stabilized copper nanoclusters with blue-emitting fluorescence

In this work, the fluorescent copper nanoclusters (Cu NCs) were firstly adopted to detect luteolin with excellent performance. The blue-emitting Cu NCs was successfully prepared through a facile one-pot approach by protection of tannic acid (TA) and chemical reduction of ascorbic acid (AA). The water-soluble nanoclusters possessed uniform size and displayed good stability. The TA-Cu NCs showed maximum luminescence at 434 nm when excited at 366 nm. Based on the static quenching and inner filter effect (IFE) mechanism, the TA-Cu NCs was efficiently and selectively quenched by luteolin. The detection limit was 0.12 μM and linear relationship existed in the range of 0.2-100 μM. Moreover, the TA-Cu NCs probe was successfully employed to detect luteolin in bovine serum samples with satisfactory recoveries. This novel platform was expected to expand the possible detection method based on fluorescence properties.

A ratiometric fluorescent sensing of proanthocyanidins by MnO2 nanosheets simultaneously tuning the photoluminescence of Au/AgNCs and thiamine

By simultaneously regulating the photoluminescence of alloy Au/Ag nanoclusters (NCs) and thiamine (VB1) through MnO₂ nanosheets (MnO₂ NS), a novel ratiometric fluorescent probe (RF-probe) was established for sensitively and selectively monitoring proanthocyanidins (PAs). The introduction of Ag (I) ions could enhance significantly the quantum yields (QYs, 11.1%) of AuNCs based on the synthetic method of UVI (UV irradiation) combined with MWH (microwave heating). MnO₂ NS could quench the fluorescence (FL) of Au/AgNCs mainly coming from Förster resonance energy transfer (FRET), while it could act as a nanozyme catalyst for directly catalyzing the oxidation of VB1 to produce highly fluorescent oxVB1. In the presence of PAs, MnO₂ was reduced to Mn²⁺, which caused that its quenching capacity and oxidase-like activity were vanished, thus the FL of oxVB1 and Au/AgNCs was reduced and recovered. The concentration of PAs could be monitored by the RF-probe with a linear range of 0.27-22.4 μmol L^-1 and corresponding limit of detection (LOD) and limit of quantification (LOQ) were calculated to be 75.9 and 250.5 nmol L^-1. Furthermore, the RF-probe was successfully used for the determination of PAs in mineral water, PAs additive and PAs capsule with satisfactory results compared to the standard HPLC method.

Dual protein ligand-modified gold nanoclusters for selective detection of serum sodium copper chlorophyllin

Precisely tuning the emission wavelength of dual ligands co-functionalized gold nanoclusters (AuNCs) presents a bright prospect for highly selective drug detection. In this study, gold nanoclusters (AuNCs) with strong red fluorescence at 633 nm were synthesized using bovine serum albumin (BSA) and bromelain (Bro) as dual ligands for highly selective detection of sodium copper chlorophyllin (SCC). Interestingly, the auto-fluorescence interference of the dual ligands was effectively avoided due to the fluorescence emission red-shifts of the prepared BSA/Bro@AuNCs; this may be mainly due to the rigid structure of the proteins. The fluorescence of BSA/Bro@AuNCs was quenched after addition of SCC, which performed well and provided a good linear calibration curve in the 5.0-25.0 μM range (R² = 0.999), and a detection limit as low as 0.5 μM. The proposed assay was further applied to the measurement of SCC in rat serums after an intravenous injection. The dual protein ligand-capped AuNCs showed great potential for drug analysis in actual biological samples.

Noble Metals Based Bimetallic and Trimetallic Nanoparticles: Controlled Synthesis, Antimicrobial and Anticancer Applications

Noble bimetallic and trimetallic nanoparticles (NBT-NPs) have superior biomedical applications as compared to their monometallic counterparts. The performance of these nanomaterials depends on their composition, shape and size. Hence, the controlled-synthesis of these nanomaterials is a hot area of research. Till date, no review article in the literature accounts regarding the controlled-synthesis and biomedical applications related to morphology, optimum composition, biocompatibility and versatile chemistry of NBT-NPs. Taking this into contemplation, an effort was made to provide a clear insight into the morphology-controlled synthesis and size/shape-dependent anticancer and bactericidal applications of NBT-NPs. Chemical reduction method for the controlled-synthesis of NBT-NPs is reviewed critically. Furthermore, the potential role of various reaction parameters such as time, reducing agents, stabilizing/capping agents, nature/concentration of precursors, temperature and pH in the shape/size-controlled synthesis of these nanomaterials are discussed. In the second part of this article, anticancer and bactericidal applications of the NBT-NPs are reviewed and the influences of optimum composition, size, surface structure, versatile chemistry and synergism are studied. Finally, the current challenges in the controlled-synthesis and biomedical applications of these nanomaterials, and prospects to resolve related issues are discussed. HighlightsChemical reduction method for the synthesis of NBT-NPs is reviewed.The influences of parameters on the control synthesis of NBT-NPs are discussed.Antibacterial and anticancer applications and cytotoxicity of NBT-NPs are reviewed.Possible solutions for the key challenges are discussed.Outlooks about the synthesis and biomedical applications of NBT-NPs are discussed.

Synthesis and characterization of maltol capped silver nanoparticles and their potential application as an antimicrobial agent and colorimetric sensor for cysteine

Maltol capped silver nanoparticles (McAgNPs) were synthesized using maltol (3-hydroxy-2-methyl-4-pyrone) as reducing and capping agent. McAgNPs were characterized by Visible and FTIR (Fourier transform infrared) spectroscopy, dynamic light scattering (DLS), and atomic force microscopy (AFM). Bright yellow color McAgNPs showed surface plasmon resonance (SPR) band at 436 nm, spherical shape and the average size between 35 to 50 nm. McAgNPs revealed higher stability against varying storage time, temperature, pH and salt concentrations. McAgNPs were successfully utilized for the selective and highly sensitive colorimetric detection of cysteine (Cys). Addition of Cys in a solution of McAgNPs, resulted a rapid change in color from yellow to orange because of the formation of nanoaggregates as confirmed by Visible/FTIR spectroscopy, DLS, and AFM studies. The estimated limit of detection (0.043 μM) was found to be more sensitive than previously reported other optical methods. The practical applicability of probe was also established by spiking the known concentrations of Cys in biological (blood plasma and urine) and environmental (tap and lake water) samples with significant recovery rates (92-104.6%). Despite being nontoxic to various tested cell lines, McAgNPs demonstrated potent antimicrobial, antibiofilm, and biofilm eradicating activities, thus potentially valuable in diagnostics and/or the synthesis of other nanocomposite material for broader applications.

Survival Mechanisms and Xenobiotic Susceptibility of Keratinocytes Exposed to Metal-Derived Nanoparticles

Metal-derived nanoparticles (Mt-NPs) are increasingly used in cosmetology due to their ultraviolet shielding (titanium dioxide [TiO₂]), antioxidant (cerium dioxide [CeO₂]), and biocidal (silver [Ag]) properties. In the absence of overt toxicity (i.e., cell death), Mt-NPs are considered safe for cosmetic applications. However, there is little understanding about the mechanisms involved in the survival of keratinocytes exposed to subtoxic levels of Mt-NPs. Human keratinocytes (HaCaT) were exposed subacutely to subtoxic concentrations (≤30 μg/mL, 48-72 h) of rutile (r) TiO₂ (cylindrical), CeO₂ (cubic) and Ag (spherical) with a core/hydrodynamic size of <50/<100 nm and >98% purity. Mt-NP uptake was indirectly quantified by changes in the light side scatter, where the kinetics (time/dose-response) suggested that the three types of Mt-NPs were similarly uptaken by keratinocytes. rTiO₂ and CeO₂, but not Ag-NPs, increased autophagy, whose inhibition prompted cell death. No increase in the steady-state levels of reactive oxygen species (ROS) was induced by exposure to any of the Mt-NPs tested. Interestingly, intracellular Ag-NP aggregates observed an increased far-red autofluorescence (≥740 nm em), which has been ascribed to their binding to thiol molecules such as glutathione (GSH). Accordingly, inhibition of GSH synthesis, but not the impairment of oxidized GSH recycling, sensitized keratinocytes to Ag-NPs suggesting that GSH homeostasis, and its direct scavenging of Ag-NPs, but not ROS, is essential for keratinocyte survival upon exposure to Ag-NP. rTiO₂ and Ag, but not CeO₂-NPs, compromised metabolic flux (glycolysis and respiration), but ATP levels were unaltered. Finally, we also observed that exposure to Mt-NPs sensitized keratinocytes to non-UV xenobiotic exposure (arsenite and paraquat). Our results demonstrate the differential contribution of autophagy and GSH homeostasis to the survival of human keratinocytes exposed to subtoxic concentrations of Mt-NPs and highlight the increased susceptibility of keratinocytes exposed to Mt-NPs to a second xenobiotic insult.

Switch on fluorescence mode for determination of l-cysteine with carbon quantum dots and Au nanoparticles as a probe

Citric acid and urea were used as precursors for the preparation of carbon quantum dots (CQDs) which exhibited a maximum emission wavelength at 515 nm when excited at 410 nm. Upon addition of citrate-stabilized Au nanoparticles (AuNPs) with the maximum absorption wavelength at 520 nm, the fluorescence of the CQDs could be efficiently quenched, attributed to the energy transfer between CQDs and AuNPs. However, the further introduction of l-cysteine (Cys) could cause the aggregation of AuNPs along with a drop in absorption at 520 nm, resulting in the fluorescence recovery of the CQDs–AuNPs system. Therefore, a simple and reliable switch on fluorescence sensing platform for determination of Cys was constructed. The significant factors, such as pH and incubation time, that affected the detection of Cys were optimized with the AuNP concentration set as 2.50 nM at room temperature. Under the optimized conditions, the fluorescence recoveries (ΔF) were strongly correlated with Cys concentration in the 0.20 to 4.0 μM range, and the detection limit is 0.012 μM. More importantly, our CQD-based sensing platform was successfully used for the detection of Cys in milk samples with high precision and accuracy, indicating the potential of the probe in practical applications.

We demonstrated a fluorescence probe composed of CQDs and AuNPs for switch on detection of Cys, where CQDs as fluorescence reporters and AuNPs as fluorescence quenchers were chosen.

Selective luminescence determination of cysteine by using terbium-modified silver nanoparticles or terbium-modified graphene quantum dots

Two methods for the luminescence determination of cysteine (Cys) are presented. They make use of either silver nanoparticles (Ag NPs) or graphene quantum dots (GQDs), both doped with terbium(III). The methods are based on the finding that Cys quenches the green luminescence of Tb(III)-Ag NPs and Tb(III)-GQDs. The excitation/emission maxima are at 306/545 and 257/545 nm, for both nanoprobes, respectively. Response is linear in the 0.28-5.0 μg mL^-1 Cys concentration range for the Tb(III)-Ag NP system, and from 0.05-3.0 μg mL^-1 for the Tb(III)-GQD system. The respective limits of detection are 0.09 and 0.015 μg mL^-1. The probes were applied to the time-resolved luminometric determination of Cys in (spiked) food supplements and gave satisfactory results. Graphical abstractSchematic representation of the quenching by cysteine (Cys) of the time-resolved luminescence (TSL) of terbium-graphene quantum dots [Tb(III)-GQD] and of terbium-silver nanoparticles [Tb(III)-Ag NP].

Fluorescence turn-on sensing of L-cysteine based on FRET between Au-Ag nanoclusters and Au nanorods

The applications of metallic nanoclusters and nanoparticles in biological sensing have attracted special attention owing to their optical interaction based on fluorescence and surface plasmon resonance (SPR). In this work, we designed a fluorescent nanoprobe for the determination of L-cysteine (L-Cys) based on fluorescence resonance energy transfer (FRET) from gold‑silver bimetallic nanoclusters (Au-Ag NCs) to gold nanorods (AuNRs). Firstly, the negatively charged Au-Ag NCs protected by bovine serum albumin (BSA) are directly adsorbed on the surface of the positively charged AuNRs through electrostatic interaction, and the FRET effect leads to distinct fluorescence quenching of Au-Ag NCs at 615nm. The SPR wavelength of AuNRs is dependent on the aspect ratio, so the SPR of AuNRs could be tuned to have a better spectral overlap with fluorescence of Au-Ag NCs, which enhances the fluorescence quenching effect. Because the SH group of L-Cys has an affinity with gold, the addition of L-Cys can result in the release of Au-Ag NCs from the surface of AuNRs via forming AuS bonds. Thus, the introduction of L-Cys could effectively restore the fluorescence emission of the AuNRs/Au-Ag NCs system because of the restraint of FRET effect. Under the optimized conditions, the fluorescence recovery of AuNRs/Au-Ag NCs probe exhibits a linear response to L-Cys concentration ranging from 5 to 100μM, and the corresponding theoretical detection limit (LOD) is 1.73μM. Meanwhile, this method displays excellent sensitivity and selectivity for L-Cys over other amino acids, and it has been successfully applied to detect L-Cys in real samples.