Super-High-Resolution Densitometry by Optical Trapping of a Single-Molecularly Imprinted Polymer Particle for Subsingle Molecule Detection.

In this study, for the first time, we have shown that the single nano-/microparticle trapping ability of optical tweezers combined with the high selectivity of molecularly imprinted polymers (MIPs) provides an indispensable molecular-level instrument for chemical sciences. Trapping a single MIP inside a solution and analyzing its Brownian motion allow for real-time determination of its target molecule [trimipramine (TMP) in our case] content. This method is also utilized to precisely measure TMP concentration in the bulk solution. The detection and optical volumes, respectively, defined as single MIP volume and laser focal volume, were about a few femtoliters. According to our data within a detection volume inside the bulk solution, 0.02-0.25 target molecules could be detectable with a detection limit of 0.005 molecules. Thus, we detected 1/1000th of the subsingle molecule in detection volume by high-resolution densitometry.

Fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS) as molecular counting of methamphetamine.

A novel and sensitive approach has been presented for the determination of methamphetamine (METH) based on fluorescence resonance energy transfer-thermal lens spectrometry (FRET-TLS). Due to the affinity of fluorescein molecules to the surface of AuNPs through the electrostatic interaction and thereby caused reduction of the distance between fluorescein and AuNPs, the best way for de-excitation of excited fluorescein is FRET. The energy absorbed by fluorescein transferred to AuNPs causes enhancement of the thermal lens effect. The thermal lens of the fluorescence molecule could be enhanced through a proper acceptor. Upon the addition of methamphetamine, the fluorescein molecules are detached from the surface of AuNPs, due to the stronger adsorption of methamphetamine. As a result, the fluorescence of fluorescein recovered, and the thermal lens effect of fluorescein decreased. The mechanism of energy transfer was evaluated by two different methods including time-resolved spectroscopy and thermal lens spectrometry. Under the optimal conditions, the thermal lens signal was linearly proportional to methamphetamine concentration in the range 5 - 80 nM. The limit of detection and limit of quantitation were 1.5 nM and 4.5 nM, respectively. The detection volume and limit of molecules in the detection volume were 960 attoliter and 87 molecules, respectively. The method was successfully applied for the determination of methamphetamine in human blood plasma and urine.

Enhancmentation of Photo-Thermal Lens of Fluorescence Molecules by Fluorescence Resonance Energy Transfer Mechanism.

The photo-thermal lens technique is based on the measurement of the gradient temperature that is produced in an illuminated sample by laser beam as a result of non-radiative relaxation. The sensitivity of photo-thermal lens is higher than conventional absorption techniques, due to the direct measurement of absorbed energy. However, the main drawback of the photo-thermal lens technique is the inability to measure molecules that release their excess energy of absorption in the form of radiation relaxation. In fluorescence molecules, because their excess energy is released by radiation, the photo-thermal lens is insignificant. In this research, we aim to increase the photo-thermal lens sensitivity of the fluorescence molecules by selecting the appropriate acceptor for the fluorescence molecules as the donor. We investigated the effect of the presence of AuNPs on the photo-thermal lens of di-triazene (DTA) as fluorescence molecules. We observed that AuNPs enhanced the photo-thermal lens of DTA. The quantum yield of DTA was calculated to be 90.45%. The energy transfer from DTA to AuNPs occurs by fluorescence resonance energy transfer (FRET) mechanism. The FRET efficiency was 83.43%. In the presence of AuNPs, the photo-thermal lens of the DTA was amplified by four times more. The calibration curve of DTA is linear in the range of 0.1 to 110 ng/mL. The limited of detection (LOD) value of 0.08 ng/mL is calculated.

Carbon dots doped by nitrogen and sulfur for dual-mode colorimetric and fluorometric determination of Fe3+ and histidine and intracellular imaging of Fe3+ in living cells.

The first dual-modality highly intensive fluorescent and colorimetric nanoprobe for Fe3+ ions and histidine is reported. The carbon dots doped by nitrogen and sulfur (N,S-CDs) prepared by the one-pot hydrothermal method have an excitation/emission wavelength of 320/420 nm with 56% quantum yield. N,S-CDs exhibit strong visible fluorescence with high stability at pH ~ 7.0. The fluorescence intensity of the N,S-CDs is quenched in the presence of Fe3+ ions which are recovered upon the addition of histidine. The addition of Fe3+ ions also induces a color change from yellow to red. Using colorimetric determination, Fe3+ and histidine exhibited linearity in the range 75-675 and 100-375 µmol L-1, respectively, while with fluorometric determinations the dynamic range was 0.1-275 and 0.1-3 µmol L-1 for Fe3+ and histidine, respectively. The limits of detection were 19 nmol L-1 and 0.03 µmol L-1 using fluorometry and 20 µmol L-1 and 24.2 µmol L-1 using colorimetry, for Fe3+ and histidine respectively. The relative standard deviations (n = 5) for Fe3+ (10 µmol L-1) and histidine (1 µmol L-1) using fluorometry were 4.6 and 7.3% and using colorimetry at 100 µmol L-1 of Fe3+ and 150 µmol L-1 of histidine were 3.2 and 5.6%, respectively. The developed fluorometric method was applied for the determination of Fe3+ and histidine in various foods and biological fluid samples as well as intracellular imaging of iron. The accuracy of the method for iron determination was confirmed by the analysis of certified reference materials (wheat flour, tomato leaves, and whole milk powder) and quality control materials (whole milk powder, serum, and urine), whereas for histidine, the accuracy was determined by recovery experiment and independent analysis. Good recovery values in ranges of 92-96% and 94-98% were achieved for Fe3+ and histidine, respectively. Graphical abstract.

Fiberoptic-Coupled Spectrofluorometer with Array Detection as a Process Analytical Chemistry Tool for Continuous Flow Monitoring of Fluoroquinolone Antibiotics.

Nowadays, there is an increasing need for sensitive real-time measurements of various analytes and monitoring of industrial products and environmental processes. Herein, we describe a fluorescence spectrometer in continuous flow mode in which the sample is fed to the flow cell using a peristaltic pump. The excitation beam is introduced to the sample chamber by an optical fiber. The fluorescence emitted upon excitation is collected at the right angle using another optical fiber and then transmitted to the fluorescence spectrometer which utilizes an array detector. The array detection, as a key factor in process analytical chemistry, made the fluorescence spectrometer suited for multiwavelength detection of the fluorescence spectrum of the analytes. After optimization of the experimental parameters, the system has been successfully employed for sensitive determination of four fluoroquinolone antibiotics such as ciprofloxacin, ofloxacin, levofloxacin, and moxifloxacin. The linear dynamic ranges of four fluoroquinolones were between 0.25 and 20 µg·mL-1, and the detection limit of the method for ciprofloxacin, ofloxacin, levofloxacin, and moxifloxacin were 81, 36, 35, and 93 ng·mL-1, respectively. Finally, the proposed system is carried out for determination of fluoroquinolones in some pharmaceutical formulations.

Bovine serum albumin determination based on methylene blue detection by photothermal lens spectroscopy.

We report on a new sensitive method, for bovine serum albumin quantification, which is based on the use of methylene blue as a labelling agent combined with photothermal lens detection. In the presence of sodium dodecyl sulfate, methylene blue forms a dimer which can react with bovine serum albumin producing dedimerization. We found that, the photothermal signal decreases proportional to the concentration of bovine serum albumin added to the system composed by dodecyl sulfate and methylene blue. Therefore, the change of the signal intensity is linearly proportional to the concentration of bovine serum albumin. Under the optimized analytical conditions, used in this work, the photothermal signal is linearly dependent on the concentration of bovine serum albumin in the range of 0.5 × 10-6-7.5 × 10-5 gmL-1 with a regression coefficient R2 = 0.9954. The relative standard deviation for BSA determination at 3.5 × 10-5 gmL-1 (n = 5) is 2.3% and the achieved detection limit is 3.5 × 10-7 gmL-1.

Plasmonic fiber optic hydrogen sensor using oxygen defects in nanostructured molybdenum trioxide film.

Hydrogen is one of the most promising candidates for fulfilling the next energy demands in transportation, aerospace, heating, and power generation. Due to its highly explosive nature, hydrogen leakage sensors are considered a critical industrial need. We propose a room-temperature, high-sensitivity hydrogen sensor using oxygen defect-induced plasmonic features. The proposed sensing probe utilizes nanostructured α-MoO3 thin film as the sensing material in which free carriers and plasmonic properties are induced in response to hydrogen exposure. A notable blue spectral shift of 70.6 nm is observed in response to hydrogen gas exposure from 150 ppm to 2000 ppm, which confirms the sensor's capability for efficient detection of low hydrogen concentrations. The sensor's sensitivity, linearity, and reversibility are experimentally investigated through a simple optical setup.

Microfluidic chip-photothermal lens microscopy for DNA hybridization assay using gold nanoparticles.

A new approach employing a microchip in combination with photothermal lens microscopy has been described for a DNA hybridization assay using gold nanoparticles. The difference in adsorption propensities of single- and double-stranded DNAs on gold nanoparticles was used for a highly sensitive DNA hybridization assay through a photothermal lens effect in a femtoliter scale of detection volume. Under the optimized conditions, the results showed that the variation of photothermal lens signal in the focal volume of 105 fL (10-15 L) was linearly proportional to the target DNA concentration over the range of 50-500 nM with detection limits of 30.7 nM and 27.3 nM for target DNA I and II, respectively. The lowest amount of target DNA that was measured using gold nanoparticles was 2.6 zepto mole. The assay was completed within 5 min and the relative standard deviations (n = 8) for both target DNAs were about 2.34%. The hybridization process was proved by two different common methods including gel electrophoresis and in situ fluorescence monitoring of DNA hybridization. The performance of this detection method was investigated in diluted human serum sample as a complex sample. The recovery values were between 98 and 104.9%. Graphical abstract.

Sensitive determination of DNA based on phosphate-dye interaction using photothermal lens technique.

Photothermal lens spectrometry is a powerful optical detection technique that can be used to investigate biomolecules. In this work, for the first time to our knowledge, photothermal lens spectrometry was used for determination of nanomolar concentrations of three distinct deoxyribonucleic acid (DNA) strands using methylene blue as a labeling dye. Methylene blue interacts with phosphate groups of the DNA in lower DNA concentrations. It was observed that phosphate-methylene blue interaction had no obvious effect on methylene blue absorption and fluorescence spectra, but the photothermal lens spectrometry signal of methylene blue increased with DNA concentration. For this purpose, to evaluate the performance of the presented method, herring sperm DNA, Escherichia coli bacteria DNA, and partial 16S rRNA genes were examined. Under optimum conditions, photothermal lens spectrometry intensity of methylene blue increased linearly with DNA concentration when herring sperm DNA, Escherichia coli DNA, and 16S rRNA gene concentrations increased in the ranges of 0.1-250, 1-700, and 1-800 nmol L-1, respectively. The corresponding detection limits were found to be 0.07, 0.71, and 0.56 nmol L-1, respectively, and relative standard deviations for 50 nmol L-1 of the tested samples were 2.59%, 4.95%, and 4.57%, respectively.

Headspace solid-phase microextraction (HS-SPME) combined with GC-MS as a process analytical technology (PAT) tool for monitoring the cultivation of C. tetani.

Vaccine production is a biological process in which variation in time and output is inevitable. Thus, the application of Process Analytical Technologies (PAT) will be important in this regard. Headspace solid - phase microextraction (HS-SPME) coupled with GC-MS can be used as a PAT for process monitoring. This method is suitable to chemical profiling of volatile organic compounds (VOCs) emitted from microorganisms. Tetanus is a lethal disease caused by Clostridium tetani (C. tetani) bacterium and vaccination is an ultimate way to prevent this disease. In this paper, SPME fiber was used for the investigation of VOCs emerging from C. tetani during cultivation. Different types of VOCs such as sulfur-containing compounds were identified and some of them were selected as biomarkers for bioreactor monitoring during vaccine production. In the second step, the portable dynamic air sampling (PDAS) device was used as an interface for sampling VOCs by SPME fibers. The sampling procedure was optimized by face-centered central composite design (FC-CCD). The optimized sampling time and inlet gas flow rates were 10 min and 2 m L s-1, respectively. PDAS was mounted in exhausted gas line of bioreactor and 42 samples of VOCs were prepared by SPME fibers in 7 days during incubation. Simultaneously, pH and optical density (OD) were evaluated to cultivation process which showed good correlations with the identified VOCs (>80%). This method could be used for VOCs sampling from off-gas of a bioreactor to monitoring of the cultivation process.

Sol-gel-based SPME fiber as a reliable sampling technique for studying biogenic volatile organic compounds released from Clostridium tetani.

A novel and efficient headspace solid-phase microextraction (HS-SPME) method, followed by gas chromatography mass spectrometry (GC-MS), was developed to study volatile organic compounds (VOCs) emerging from microorganisms. Two homemade SPME fibers, a semi-polar poly (dimethylsiloxane) (PDMS) fiber, and a polar polyethylene glycol (PEG) fiber, along with two commercial fibers (PDMS and PDMS/DVB) were used to collect VOCs emerging from Clostridium tetani which was cultured in different media. The adsorbed VOCs were desorbed and identified, in vitro, using GC-MS. The adsorption efficiency was improved by optimizing the time duration of adsorption and desorption. About 50 components were identified by the proposed method. The main detected compounds appeared to be sulfur containing compounds such as butanethioic acid S-methyl ester, dimethyl trisulfide, and dimethyl tetrasulfide. These volatile sulfur containing compounds are derived from amino acids containing the sulfur element, which probably coexist in the mentioned bacterium or are added to the culture media. The developed HS-SPME-GC-MS method allowed the determination of the chemical fingerprint of Clostridium tetani volatile constituents, and thus provides a new, simple, and reliable tool for studying the growth of microorganisms. Graphical abstract Investigation of biogenic VOCs released from Clostridium tetani using SPME-GC-MS.

Laser induced thermal lens microscopy for highly sensitive determination of captopril.

In this work, a combined flow injection-photo thermal lens microscopy (FI-PTLM) system was used for highly sensitive determination of captopril as an angiotensin-converting enzyme inhibitor. Captopril has no absorption in the visible range, but due to its thiol group could interact with gold nanoparticles (GNPs). GNPs, because of their surface plasmon resonance (SPR), have absorption in the visible range, but their interaction with a low concentration of captopril shows no effective change in UV-Vis spectrophotometry because their aggregation is slight. On the contrary, at the same condition, the PTLM with a visible light source enables sensitive measurement of this compound. The thiol group of captopril binds to the surface of GNPs and decreases the SPR. At the optimum condition in the focal volume of 2.68 fL (f=10-15), the obtained range of linearity was 50-800 nM. The developed method was successfully applied for the determination of captopril in human serum and pharmaceutical samples.

Laser induced-thermal lens spectrometry in combination with dispersive liquid-liquid microextraction for trace analysis.

A new combination method including laser induced-thermal lens spectrometry (LI-TLS) and dispersive liquid-liquid micro extraction (DLLME) was developed and used for determination and preconcentration of trace amount of lead in liquid samples. Thermal lens spectrometry is suitable for determination of analyte after DLLME because of the low volume of the remained phase after DLLME and increasing of the enhancement factor for the non polar organic solvents. Non polar organic solvents have the ideal conditions for this combination because of low thermal conductivity and large variation in refractive index with temperature. In this method; ethanol, carbon tetrachloride and 1,5-diphenyl thiocarbazone (dithizone), were used as disperser solvent, extraction solvent and chelating agent, respectively. Some effective parameters on the micro extraction, complex formation and combination were selected and optimized. Under optimum conditions, the calibration graphs were linear in the range of 0.1-75 µg L(-1) with the detection limit of 0.01 µg L(-1). The relative standard deviation (RSD) for 5 and 50 µg L(-1) of lead was 3.2 and 2.5, respectively. The enhancement factor of 1000 was obtained from a sample volume of 10.0 mL and determination volume of 25 µL. DLLME/LI-TLS method was applied to the analysis of human blood serums and real water samples. Accuracy of the method was proved by using of standard reference materials. Also, the proposed method was compared with other trace analysis methods.

Laser induced thermal lens spectrometry for cobalt determination after cloud point extraction.

A new approach, employing cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS), has been developed for the determination of cobalt. The CPE and TLS methods have good matching conditions for combination because TLS is suitable for low volume samples obtained after CPE and for organic solvents, which are used for dissolving the remaining analyte phase. 1-(2-Pyridylazo)-2-naphthol (PAN) was used as a complexing agent and octylphenoxypolyethoxyethanol (Triton X-114) was added as a surfactant; then the pH of solution was adjusted. After phase separation at 50 degrees C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 microL of carbon tetrachloride. The obtained solution was introduced into the quartz micro cell and the analyte was determined by thermal lens spectrometry. The He-Ne laser (632.8 nm) was used as both the probe and the excite source. Under optimum conditions, the analytical curve was linear for the concentration range of 0.2-40 ng mL(-1) and the detection limit was 0.03 ng mL(-1). The enhancement factor of 470 was achieved for a 10 mL sample. Relative standard deviations were lower than 5%. The method was successfully applied to the extraction and determination of cobalt in tap, river and sea water.