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In this study, gold-coated quartz tuning forks (QTFs) sensing devices functionalized with self-assembled monolayers (SAM) of a lower-rim functionalized calix[4]arene methoxy ester were used for the detection of divalent Ca2+ and Pb2+ ions in aqueous solutions by utilizing adsorption behavior and the radiative effect. The gold-coated QTF functionalized calix[4]arene methoxy ester sensing device was tested by measuring the respective frequency shifts obtained using small (60 µL) samples of aqueous PbCl2 at two different concentrations (10−6 and 10−4 M). For 10−4 M solutions of PbCl2, results showed that the resonance frequency shift Δf = 317 Hz, from 32,867 Hz (fCalix) to 32,550 Hz (fCalix⊃Pb2+) due to the absorption of lead (Pb2+) ions (10-4 M) by calixl[4]arene methoxy ester receptor molecules on the QTF sensing layer from the aqueous solution to forming the ([Calix ⊃ Pb2+]) complex. The most significant frequency changes were observed at a concentration of 10−6 M CaCl2, where CaCl2 exhibited the biggest change of 356 Hz, from 32,893 Hz (fCalix) to 32,537 Hz (fCalix⊃Ca2+), compared to 317 Hz for PbCl2 (10−4 M). The limit of detection was 100 femtomolar (fM) for CaCl2 and 245 fM for PbCl2. After that, we irradiated the receptor molecules which was holding Pb2+ ions in the complex ([calix ⊃ Pb2+]) on the QTF sensing layer with a radiation dose ranging from 7.5 to 50 µGy of gamma rays from the Cesium-137 source for 30 min. Interestingly, it was observed that the resonance frequency shift (Δf = 54 Hz) back to 32,604 Hz from 32,550 Hz (f(Calix⊃Pb2+)), which strongly suggests that the Pb2+ ion removed from ([calix ⊃ Pb2+]) complex on the QTF sensing layer due to gamma radiation dose. To follow up on the radiation effect of the ([calix ⊃ Pb2+]) on the QTF sensing layer, we stopped the gamma radiation source and kept it for an additional 10 min to see if there was any resonance frequency. It was noticed that an additional resonance frequency shifted (Δf = 33 Hz) back to 32,637 Hz from 32,604 Hz after stopping the gamma radiation source for 10 min. We assume that the complex ([calix ⊃ Pb2+]) absorbs the gamma radiation and continues the removal of Pb2+ ions from the complex on the sensing layer. A similar phenomenon was also observed for the absorption of lead (Pb2+) ions (10-6 M) by calix[4]arene methoxy ester receptor molecules on the QTF sensing layer from the aqueous solution to forming the ([Calix ⊃ Pb2+]) complex. The resonance frequency shift Δf = 142 Hz, from 32,706 Hz (fCalix) to 32,564 Hz (fCalix⊃Pb2+) due to the absorption of lead (Pb2+) ions (10-6 M) by calix[4]arene methoxy ester receptor molecules on the QTF sensing layer from the aqueous solution to forming the ([Calix ⊃ Pb2+]) complex. Subsequent exposure to gamma radiation, with doses ranging from 7.5 to 50 µGy from a Cesium-137 source over 30 min, prompted a resonance frequency shift (Δf = 37 Hz) back to 32,606 Hz from 32,564 Hz (f(Calix⊃Pb2+)). This shift strongly suggests the removal of Pb2+ ions from the ([calix ⊃ Pb2+]) complex on the QTF sensing layer due to gamma radiation dose. X-ray photoelectron spectroscopy (XPS) analysis confirmed the chemical adsorption of Pb2+ ions onto the gold-coated QTFs functionalized calix[4]arene adsorbent sensing layer surface. Therefore, the technology underlying the calix[4]arene-functionalized sensing device holds promise for diverse industrial applications, supporting potential advancements in water pollution mitigation through the proposed adsorption and irradiation mechanism.

Despite the expected direct effects of radiation on DNA through its direct interaction with the biomolecule, research indicates that radiation also interacts with the DNA’s environment, resulting in indirect effects. Therefore, in this study, we explored the feasibility of using the quartz tuning fork (QTF) sensor system in biomedical applications, specifically in detecting DNA damage caused by low doses of gamma radiation, directly and indirectly. We differentiated between direct and indirect damage by analyzing the fork’s resonance frequency changes. This experiment was divided into three stages: before, during, and after irradiation. Each stage involved samples of pure DNA and DNA in a 60-µL aqueous solution, evaluated under identical conditions. Before irradiation, we measured frequency shifts (Δf) over a 20-min period, resulting in values of 19.34, 20.25, and 7.6 Hz for water, DNA, and DNA in water, respectively. Subsequently, the samples were irradiated with cesium-137 for the specified duration, resulting in frequency shifts of ∼ 39.21, 28.37, and 41.23 Hz for the same conditions. Our investigations showed an increase in Δf from 20.25 to 28.3 Hz at doses ranging from 7.5 to 30 µGy for pure DNA. Interestingly, DNA in aqueous solution exhibited hypersensitivity to radiation, with frequency shifts ranging from 7.6 to 41.23 Hz. Furthermore, we observed a significant difference in frequency shift after irradiation between pure DNA and DNA in water, with shifts of ∼ 70.75–98.45 Hz and 56.32–79.28 Hz for DNA and DNA in water, respectively. This result indicates a significant increase in DNA damage in aqueous environments, driven by the generation of active hydroxyl radicals (OH−), resulting in base damage and an associated increase in strand breaks. Consequently, our research indicates a lack of substantial direct impact on DNA repair owing to the absence of a conducive postirradiation environment. Therefore, QTF is a valuable biomarker for radiation sensitivity and is promising for future applications as a mass-sensitive biosensor.

The ongoing global concern of cancer worldwide necessitates the development of advanced diagnostic and therapeutic strategies. The majority of recent detection strategies involve the employment of biomarkers. A critical biomarker for cancer immunotherapy efficacy and patient prognosis is Programmed Death Ligand 1 (PD-L1), which is a key immune checkpoint protein. PD-L1 can be particularly linked to cancer progression and therapy response. Current detection methods, such as enzyme-linked immunosorbent assay (ELISA), face limitations like high cost, time consumption, and complexity. This study introduces a microcantilever-based biosensor designed for the detection of soluble PD-L1 (sPD-L1), which has a specific association with PD-L1. The biosensor utilizes anti-PD-L1 as the sensing layer, capitalizing on the specific binding affinity between anti-PD-L1 and sPD-L1. The presence of the sensing layer was confirmed through Atomic Force Microscopy (AFM) and contact angle measurements. Binding between sPD-L1 and anti-PD-L1 induces a shift in the microcantilever's resonance frequency, which is proportional to the PD-L1 concentration. Notably, the resonance frequency shift demonstrates a robust linear relationship with the increasing biomarker concentration, ranging from 0.05 ng/ml to 500 ng/ml. The detection limit of the biosensor was determined to be approximately 10 pg/ml. The biosensor demonstrates excellent performance in detecting PD-L1 with high specificity even in complex biological matrices. This innovative approach not only provides a promising tool for early cancer diagnosis but also holds potential for monitoring immunotherapy efficacy, paving the way for personalized and effective cancer treatments.

Quartz tuning fork (QTF) sensors are widely used in various sensing applications due to their high sensitivity, stability, and accuracy. This study explores the functionalization of QTF sensors with a thin coating of polydopamine which can be used a molecular receptor for specific analytes. Dopamine is a neurotransmitter that plays a critical role in the brain's reward and pleasure centers, has been shown to have unique chemical and physical properties that make it a valuable functionalization agent for sensing applications. The functionalized QTF sensors were characterized using measurements of their resonance frequency which is an indication of coated mass of dopamine on the individual prongs of the QTF sensors. Additionally, the coatings were characterized through scanning electron microscopy and Fourier-transform infrared spectroscopy. The performance of the functionalized sensors was evaluated by measuring their response to various thickness of the polydopamine coating.

Vitamin D deficiency or insufficiency is a growing public health problem. In this work, a novel and sample approach based on microcantilever for measuring the level of 25-hydroxyvitamin D (25(OH)D) was proposed. The Bruno aptamer was utilized to functionalize the microcantilevers, serving as a sensing layer for detecting 25(OH)D. The working principle of the sensor is based on the changes of the microcantilever deflection and frequency as a result of the aptamer removal from the surface of the microcantilever resulting from its interaction with vitamin D. The results showed a linear dependence between vitamin D concentration and the microcantilever deflection and frequency shift in a range of concentrations from 1 to 300 nM. For this biosensor, the limit of detection (LOD) was calculated to be ∼ 0.3 nM. The biosensor selectivity was tested against vitamin C and the sensor showed high selectivity towards vitamin D.

Undoped and doped polyvinyl pyrrolidone/ carboxymethyl cellulose (PVP/CMC: 50/50%) blended polymers with melanin were formed. X-ray diffraction analysis confirmed the amorphous nature of all blends. Scanning electron microscopy results confirmed the smooth and homogeneous surface of the undoped and doped PVP/CMC blend with melanin. The optical parameters and fluorescence spectra of the PVP/CMC blend were investigated as functions of melanin content. The direct optical band gap (Eg) for the used melanin is 2.86 eV. The direct and indirect Eg values for the PVP/CMC blend are 5.1 and (4.9, 3.2) eV, respectively. The direct and indirect Eg values were reduced to (4.5, 3.23) and (2.2, 1.33) eV as the amount of melanin became 3 wt % in the doped blend. The effect of melanin doping on the dielectric constant, dielectric loss, AC conductivity, complex impedance, Nyquist plot of the complex impedance, and electric modulus of the PVP/CMC blend was also studied.

Abstract The human cytomegalovirus (HCMV) is an asymptomatic common virus that is typically harmless, but in some cases, it can be life threatening. Thus, there is an urgent need to develop novel diagnostic methods and strengthen the efforts to combat this virus. A microcantilever‐based biosensor functionalised with the UL83‐antibody of HCMV (UL83‐HCMV antibody) has been developed to detect the UL83‐antigen of HCMV (UL83‐HCMV antigen) at different concentrations ranging from 0.3 to 300 ng/ml. The response of the biosensor to the presence of UL83‐HCMV antigen was measured through the shift in resonance frequency before and after antigen–antibody binding. The system shows a low detection limit of 84 pg/ml, which is comparable to traditional sensors, and a detection time of less than 15 min was achieved. The selectivity of the sensor was demonstrated using three different proteins with and without the UL83‐HCMV antigen. The biosensor shows high selectivity for the UL83‐HCMV antigen. Mass loading by the UL83‐HCMV antigen was roughly estimated with a sensitivity of ∼30 fg/Hz. This technique is crucial for the fabrication of portable and low‐cost biosensors that can be used in real‐time monitoring and enables early medical diagnosis.

Abstract Diagnosis and monitoring of glucose level in human blood has become a prime necessity to avoid health risk and to cater this, a sensor’s performance with wide linearity range and high sensitivity is required. This work reports the use of ternary composite viz. MG–Cu2O (rGO supported MXene sheet with Cu2O) for non-enzymatic sensing of glucose. It has been prepared by co-precipitation method and characterized with X-ray powder diffraction, Ultraviolet–visible absorption spectroscopy (UV–Vis), Raman spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy and Selected area diffraction. These analyses show a cubic structure with spherical shaped Cu2O grown on the MG sheet. Further, the electrocatalytic activity was carried out with MG–Cu2O sensing element by cyclic voltammetry and chronoamperometry technique and compared with M–Cu2O (MXene with Cu2O) composite without graphene oxide. Of these, MG–Cu2O composite was having the high defect density with lower crystalline size of Cu2O, which might enhance the conductivity thereby increasing the electrocatalytic activity towards the oxidation of glucose as compared to M–Cu2O. The prepared MG–Cu2O composite shows a sensitivity of 126.6 µAmM−1 cm−2 with a wide linear range of 0.01to 30 mM, good selectivity, good stability over 30 days and shows a low Relative Standard Deviation (RSD) of 1.7% value towards the sensing of glucose level in human serum. Thus, the aforementioned finding indicates that the prepared sensing electrode is a well suitable candidate for the sensing of glucose level for real time applications.

Human cytomegalovirus (HCMV) possess great threat to immunocompromised patients and pregnant women since It can cause disability if left untreated. Especially for unborn babies, if the virus was not detected at early stages, it can cause disabilities as the baby develops. Furthermore, the virus can be asymptomatic, hence, low-cost and rapid detection techniques are desirable. Currently available detection techniques of the virus are labor intensive and demand experienced technicians. For these reasons, new detection techniques are needed to overcome the current challenges associated with conventional techniques. In this work, quartz tuning fork (QTF)-based biosensor was developed for the detection of UL83-antigen of HCMV for the first time. Firstly, QTF coated with gold was functionalized with cysteamine and glutaraldehyde for UL83-antibody immobilization at the QTF surface. Then, the biosensor was tested against a variety of UL83-antigen concentrations. As the UL83-antigen concentration increased, the measured resonance frequency decreased due to increased mass loading at the QTF surface. The sensitivity of the biosensor is 15.91 Hz/ln(ng/mL). Whereas the limit of detection is 0.36 ng/mL. The biosensor showed comparable biosensing performances to those available in the literature. Furthermore, the biosensor demonstrated its selectivity towards UL83-antigen when tested against samples containing a mixture of biomarkers. The reported work demonstrates a platform for the direct and low-cost mass screening of diseases.

The quantitative evaluation of bacterial populations is required in many studies, particularly in the field of microbiology. The current techniques can be time-consuming and require a large volume of samples and trained laboratory personnel. In this regard, on-site, easy-to-use, and direct detection techniques are desirable. In this study, a quartz tuning fork (QTF) was investigated for the real-time detection of E. coli in different media, as well as the ability to determine the bacterial state and correlate the QTF parameters to the bacterial concentration. QTFs that are commercially available can also be used as sensitive sensors of viscosity and density by determining the QTFs’ damping and resonance frequency. As a result, the influence of viscous biofilm adhered to its surface should be detectable. First, the response of a QTF to different media without E. coli was investigated, and Luria–Bertani broth (LB) growth medium caused the largest change in frequency. Then, the QTF was tested against different concentrations of E. coli (i.e., 102–105 colony-forming units per milliliter (CFU/mL)). As the E. coli concentration increased, the frequency decreased from 32.836 to 32.242 kHz. Similarly, the quality factor decreased with the increasing E. coli concentration. With a coefficient (R) of 0.955, a linear correlation between the QTF parameters and bacterial concentration was established with a 26 CFU/mL detection limit. Furthermore, a considerable change in frequency was observed against live and dead cells in different media. These observations demonstrate the ability of QTFs to distinguish between different bacterial states. QTFs allow real-time, rapid, low-cost, and non-destructive microbial enumeration testing that requires only a small volume of liquid sample.

Microchannel resonators containing a miniaturized volume of a solution can have various applications in different fields. In this study, a microchannel cantilever was loaded with a solution containing a very small number of Pseudomonas fluorescens bacteria suspended in M9 growth medium. The liquid-filled microchannel cantilever was irradiated with a 532-nm laser. The shift in the frequency of the cantilever due to varying bacterial loads is less reliable; therefore, it could not be used for monitoring the bacterial concentration. The energy loss of the cantilever extracted from the quality factor exhibited reliable results and a very strong correlation with the bacterial concentration. The results showed a linear relation between the damping factor of the cantilever and the bacterial concentration. Accordingly, these findings were expected because the bacteria inside the solution can be considered as particles acting against the cantilever motion due to the solution’s viscosity. Thus, more bacteria caused more damping, in agreement with the experimental observations. A semiquantitative experiment was conducted with a heat source (i.e., laser beam) that focused at the cantilever tip to demonstrate the redistribution of the bacterial load within the solution due to the thermal gradient.

In this study, a sensing device employing a gold-coated quartz tuning fork (QTF) modified with a self-assembled monolayer (SAM) of L-cysteine was evaluated for the sensitive detection of Cu2+ ions in aqueous solutions. Three copper (II) salts, CuSO4, CuCl2, and Cu(NO3)2, at four different concentrations (10−12, 10−10, 10−8, and 10−6 M) in small (100 μL) water sample amounts were each used as analytes to investigate the influence of their counterions in the detection of the Cu2+ ions. It was found that, among the counterions, the sulfate anion had the largest effect upon the detection of Cu2+ in water, in the following order: SO42− > Cl− > NO3−. The lower limit of detection of the Cu2+ ions detected was in the 10−12 M range. The frequency shifts measured with the QTFs relative to deionized water were inversely proportional to the concentration/mass of the analytes. Density functional theory calculations were conducted to understand the effect of the counterions on the respective electronic interaction energies for the apparent host–guest binding of the analytes with L-cysteine and with gold surface-bound L-cysteine molecules. Gas phase (both with and uncorrected BSSE) and solution phase interaction energies (ΔIE) calculated at the B3LYP/LANL2DZ and ωB97XD levels of theory showed that the stability for the complexes were in the following order: [L-cysteine]⊃[CuSO4] > [L-cysteine]⊃[CuCl2] > [L-cysteine]⊃[Cu(NO3)2], which supports our experimental findings, as they were in the same order as the experimentally observed order for the copper salts tested: CuSO4 > CuCl2 > Cu(NO3)2.

Micromechanical sensors, in which the sensor response is created as a result of molecular interactions on the sensors’ surfaces, have been employed as a powerful technique for rapid and sensitive detection of low concentrations of chemical and biological materials. In the study reported herein, poly(methyl methacrylate) (PMMA)-coated microcantilever (MCL) sensors were used to detect the vapors of volatile alcohols (methanol, ethanol, and isopropanol) at three different concentrations. A vapor generator was used to generate and flow the alcohol vapor onto the PMMA coated MCL surface in a closed system chamber. The vapor adsorption onto the MCL surface results in a rapid and measurable deflection of the MCL. No significant deflections of the uncoated MCL occurred when the different vapors were passed through into the microcantilever chamber. Linear concentration–deflection responses were observed, with the highest sensitivity shown with methanol, followed by ethanol and then isopropanol. Density functional theory (DFT) quantum chemical calculations were conducted to estimate the electronic interaction energies (ΔIE) between the alcohol molecules and MMA and two different model tetrameric segments of PMMA. The computed ΔIEs were in the same order as the experimentally observed order: methanol > ethanol > isopropanol.

Poly(2‑(tert-butylamino)ethyl methacrylate) brushes (PTBAEMA) are grown from mesoporous silica nanoparticles via surface-initiated atom transfer radical polymerization (SI-ATRP). Linear PTBAEMA brushes are protonated and highly swollen at low pH; brushes are collapsed at pH higher than 7.7 due to deprotonation, as determined by dynamic light scattering (DLS). Quaternization of these brushes is conducted using 2-iodoethanol in alkali media. DLS measurement of nanoparticles shows that surface-confined quaternization occurs and produces pH-responsive brushes with a hydrophobic upper surface. Variation of the 2-iodoethanol reaction time enables the mean degree of surface quaternization. The pH-responsive behaviour of quaternized PTBEAMA brushes at 1 h reaction time indicates low degrees of surface quaternization, dictated by the spatial location of 2-iodoethanol. Almost uniformly quaternized brushes prepared when the conducted for 3 h and became less swollen at low pH than brushes that conducted for 1 h. The intensity of the C − C − O component (286.5 eV) in the C1s X-ray photoelectron spectrum increased, suggesting that the reaction with iodoethanol was successful occurred.