Cellulose acetate/MOF film-based colorimetric ammonia sensor for non-destructive remote monitoring of meat product spoilage.

Herein, we designed an on-site and portable colorimetric assay using cellulose acetate polymeric films incorporated with HKUST-1 metal-organic framework while immersed in a solution of methyl red and brilliant cresyl blue organic dyes as an indicator for monitoring ammonia levels. Ammonia serves as a significant biomarker of food spoilage which falls under the category of volatile organic compounds (VOCs). The designed colorimetric solid-state sensor was comprehensively characterized using FE-SEM, EDS-mapping, XRD, FTIR, and contact angle analyses. The results confirmed the superior stability, water permeability, good crystallinity and desirable morphology of the prepared sensor platform. Additionally, customized smartphone was developed and applied for online signaling and colorimetric analysis. The findings demonstrated two linear ranges: 1-100 ppb and 0.1-1340 ppm with a detection limit of 0.02 ppm. The solid-state sensor exhibited high selectivity in the presence of other VOCs such as methanol, ethanol, acetone, 2-propanol, toluene, humidity, and hexane. It displayed acceptable repeatability in both inter-day (RSD = 3.38 %) and intraday (RSD = 3.86 %), long-term stability over 4 days as well as reusability over 3 cycles. We successfully applied this sensing platform for ammonia monitoring in spoiled meat foods including veal, fish and chicken. The results indicated favorable percentage recovery and repeatability, confirming the feasibility and potential applicability of this intelligent packaging system for monitoring freshness. The platform allows for real-time monitoring and data analysis via smartphone-based online signaling, providing a convenient and effective method for ensuring food quality.

Molecular Imprinted Poly(2,5-benzimidazole)-Modified VO2-CuWO4 Homotype Heterojunction for Photoelectrochemical Dopamine Sensing.

A photoactive molecularly imprinted poly(2,5-benzimidazole)-modified vanadium dioxide-cupric tungstate (VO2-CuWO4) as an efficient photosensitive n-n type-II heterojunction thin film was electrochemically deposited on Ti substrate for the selective and robust photoelectrochemical (PEC) bioanalysis of dopamine (DA). The optical absorption of n-VO2/n-CuWO4 type-II heterojunction was capably broadened toward the visible region, which permitted superior light-harvesting and robust carriers generation, separation, and transfer processes significantly enhancing the anodic photocurrent, as confirmed by a series of PEC analyses. Findings revealed that the as-prepared label-free MIP-PEC sensor can quantitatively monitor DA in a linear range of 1 nM to 200 µM with a detection limit of 0.15 nM. This MIP-PEC sensor showed robust selectivity under conditions with high concentrations of interfering substances, which can be recovered in the real samples of urine, cocoa chocolate, and diluted yogurt, indicating its promising potential applications in biological and food samples. This work not only featured the use of photoelectrically active MIP/VO2-CuWO4 for PEC detection of DA, but also provided a new horizon for the design and implementation of functional polymers/metal oxides heterojunction materials in the field of PEC sensors and biosensors.

Ru-containing magnetic yolk-shell structured nanocomposite: a powerful, recoverable and highly durable nanocatalyst.

A novel method was used to prepare a magnetic phenylene-based periodic mesoporous organosilica nanocomposite with yolk-shell structure (Fe3O4@YSPMO). The Fe3O4@YSPMO nanomaterial was prepared by using easily accessible pluronic-P123 and cetyltrimethylammonium bromide (CTAB) surfactants under basic conditions. This material was employed for effective immobilization of potassium perruthenate to prepare an Fe3O4@YSPMO@Ru nanocatalyst for the aerobic oxidation of alcohols. The physiochemical properties of the designed Fe3O4@YSPMO@Ru nanocomposite were studied using PXRD, FT-IR, TGA, SEM, TEM, ICP, VSM and XPS analyses. Fe3O4@YSPMO@Ru was effectively employed as a highly recoverable nanocatalyst in the selective aerobic oxidation of alcohols.

L-phenylalanine-imprinted polydopamine-coated CdS/CdSe n-n type II heterojunction as an ultrasensitive photoelectrochemical biosensor for the PKU monitoring.

A simple and highly sensitive photoelectrochemical biosensor towards L-phenylalanine, as a kind of typical essential amino acid and phenylketonuria biomarker was developed on a surface molecular imprinted (MIP) polydopamine-coated CdS/CdSe/Zn heterojunction. Hierarchical marigold flower-like Zn layer decorated by n-type dichalcogenides interfacial heterojunction was successfully designed and synthesized on Ti foil for PEC converter by in situ electrodeposition. A visible-light-driven molecular imprinting film was prepared through the electropolymerization of dopamine in the presence of L-Phe as biomarker. The combination of bio-MIP and photoelectrochemistry overcomes the defects of the PEC method, which is the absence of selectivity, and offers a new PEC sensor with high sensitivity and selectivity based on visible-light-driven heterojunction and biopolymer-enhanced strategy. The unique interfacial between the Zn marigold flower layer as low work function support and CdS/CdSe n-n heterojunction as well as n-type characteristics of polydopamine imprinted by L-Phe biomarker drastically increase the light trapping and absorption in the visible range, and dramatically inhibit the charge carrier recombination, which is crucial for boosting the Bio-PEC activity. Photocatalytic, electrocatalytic and physicochemical properties of the above-mentioned layers were fully characterized. As-prepared PEC biosensor displayed superb performance for the detection of L-Phe biomarker in the optimized condition obtained from central composite design modeling, showing two linear range 0.005-2.5 and 2.5-130 µM and a low detection limit of 0.9 nM. This work suggests that such L-Phe-imprinted polydopamine-coated Zn/CdS/CdSe heterojunction is greatly promising for being applied in photoelectrochemical biosensing with high photo-electron conversion efficiency.

Colorimetric determination of F-, Br- and I- ions by Ehrlich's bio-reagent oxidation over enzyme mimic like gold nanoparticles: Peroxidase-like activity and multivariate optimization.

Citrate and polyvinyl alcohol capped gold nanoparticles (PVA-GNPs) were synthesized via chemical reduction technique and fully characterized by DLS, SEM, EDS, XRD, UV-Vis and FT-IR analysis. A simple and practical colorimetric sensor based on red-ox reaction of p-dimethylaminobenzaldehyde (DABA) as ehrlich's bio-reagent and Au(III) with H2O2 on PVA-GNPs mimic catalyst with enzyme-like activity, has been fabricated for determination of F-, Br- and I- halide anions. Prepared PVA-GNPs, can simultaneously catalyze the disintegration of H2O2, that used to reduce Au(III) ions into co-doped Au-NPs and oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent while in the presence of halide ions Au-X complex can be formed and improved sensor selectivity. Halide ions (F-, Br- and I-) effectively diminishes the catalytic activity of GNPs to disintegrate oxygenated water by the interaction among Au+ and Au0 and suppressing oxidation of p-dimethylaminobenzaldehyde ehrlich's bio-reagent. In this system which contains PVA-GNPs, H2O2, p-dimethylaminobenzaldehyde ehrlich's bio-reagent, and Au(III), increasing the halide ions (F-, Br- and I-) concentration show color changes from deep green to red. In view of this rule, in this work, a novel colorimetric technique for sensitive determination of F-, Br- and I- was developed. This method has the detection limits of 2.60 × 10-6 M, 6.64 × 10-8 M and 9.93 × 10-9 M and linear ranges between 1.98 × 10-5-1.22 × 10-3 M, 1.99 × 10-6-2.0 × 10-4 M and 1.07 × 10-7- 2.86 × 10-5 M for F-, Br- and I-, respectively. Assays are highly selective over other ions. They effectively applied to detection of halide ions in real water samples.

Photo-Sensitive Pb5S2I6 crystal incorporated polydopamine biointerface coated on nanoporous TiO2 as an efficient signal-on photoelectrochemical bioassay for ultrasensitive detection of Cr(VI) ions.

An ultrasensitive Visible light-triggered photoelectrochemical (PEC) sensor was designed based on ideal photoactive lead sulfoiodide (Pb5S2I6) as low band gap crystal, which hydrothermally synthesized rapidly at low temperature (160 °C) in hydrochloride acid media followed by its incorporation into polydopamine as reactive photo-biointerface, through a facile in situ electropolymerization method, coated on nanoporous TiO2 grown by anodization on Ti foil. The structure of as-prepared samples and their photoelectrochemical properties were fully characterized. This unique photo-sensitive Pb5S2I6 catalyst-based PEC bioassay was constructed for the detection of low-abundant Cr(VI) ion in real samples. Applying central composite design, individual and mutual interaction effects were evaluated to obtain optimized solution pH, applied potential and radiant light wavelength as operational factors influencing the PEC efficiency for Cr(VI) detection. At optimal condition, the proposed sensor due to effective suppress in electron-hole recombinations showed a very low detection limit of 3.0 nM, over a broad linear concentration range of 0.01-80 µM in addition to high sensitivity versus 1.9 µA/µM Cr(VI). Proposed PEC sensor displayed high selectivity, reproducibility and stability as well as improved excitation conversion efficiency, which make it highly applicable using solar energy. The potential applicability of the designed sensor was evaluated in water, tomato juice and hair color.

Facile Synthesis of Mixed Metal-Organic Frameworks: Electrode Materials for Supercapacitors with Excellent Areal Capacitance and Operational Stability.

Electrode materials with high surface area, tailored pore size, and efficient capability for ion insertion and enhanced transport of electrons and ions are needed for advanced supercapacitors. In the present study, a mixed metal-organic framework (MOF) (cobalt- and manganese-based MOF) was synthesized through a simple one-pot solvothermal method and employed as the electrode material for the supercapacitor. Notably, a Co-Mn MOF electrode displayed a large surface area and excellent cycling stability (over 95% capacitance retention after 1500 cycles). Also, superior pseudocapacitive behavior was observed for the Co-Mn MOF electrode in the KOH electrolyte with an exceptional areal capacitance of 1.318 F cm-2. Moreover, an asymmetric supercapacitor was assembled using Co-Mn MOF and activated carbon electrode as positive and negative electrodes, respectively. The fabricated supercapacitor showed a specific capacitance of 106.7 F g-1 at a scan rate of 10 mV s-1 and delivered a maximum energy density of 30 W h kg-1 at 2285.7 W kg-1. Our studies suggest the Co-Mn MOF as promising electrode materials for supercapacitor applications.

A simple ultrasensitive electrochemical sensor for simultaneous determination of gallic acid and uric acid in human urine and fruit juices based on zirconia-choline chloride-gold nanoparticles-modified carbon paste electrode.

The determination of gallic acid (GA) and uric acid (UA) is essential due to their biological properties. Numerous methods have been reported for the analysis of GA and UA in various real samples. However, the development of a simple, rapid and practical sensor still remains a great challenge. Here, a carbon paste electrode (CPE) was modified by nanocomposite containing zirconia nanoparticles (ZrO2NPs), Choline chloride (ChCl) and gold nanoparticles (AuNPs) to construct ZrO2-ChCl-AuNPs/CPE as electrochemical sensor for the simultaneous electro-oxidation of GA and UA. Characterization was performed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The modified electrode was investigated by different methods including electrochemical impedance spectroscopy and cyclic voltammetry. Kinetic parameters such as charge transfer coefficient, standard heterogeneous electron transfer rate constant and other parameters were calculated via voltammetry techniques. Differential pulse voltammetry was used for simultaneous determination of GA and UA applying the ZrO2-ChCl-AuNPs/CPE electrode. At the optimum conditions, this sensor showed a linear response in the ranges 0.22- 55 and 0.12-55 µM for GA and UA, respectively. In addition, low detection limits of 25 and 15 nM were obtained for GA and UA, respectively. Furthermore, ZrO2-ChCl-AuNPs/CPE was successfully applied for the independent determination of GA in green tea and fruit juice as well as the simultaneous determination of GA and UA in human urine samples.

Sonochemical-assisted synthesis of CuO/Cu2O/Cu nanoparticles as efficient photocatalyst for simultaneous degradation of pollutant dyes in rotating packed bed reactor: LED illumination and central composite design optimization.

CuO/CuO2/Cu nanoparticles were prepared by sonochemical combined thermal synthesis method and used as new photocatalyst for simultaneous photocatalytic degradation of safranin O (SO) and methylene blue (MB) dyes in rotating packed bed reactor equipped to blue light emitting diode (LED). The physicochemical properties of the synthesized CuO/Cu2O/Cu nanoparticles were investigated by XRD, SEM and DRS analysis. The band-gap of the prepared CuO/Cu2O/Cu-NPs was estimated to be about 1.42eV which is appropriate for photodegradation process under blue light irradiation. In rotating packed bed reactors, two key parameters are very important, one high centrifugal field and other porous media, which intensify mass transfer operation leads to photodegradation improvement. The maximum photodegradation efficiency was obtained at pH of 6 and subsequently the effects of CuO/Cu2O/Cu-NPs dosage, rotational speed, initial dyes concentration, flow rate and reaction time were studied by central composite design (CCD) and optimized values were found to be 0.3g/L, 900rpm, 10mg/L of both dyes, 0.3L/min and 90min, respectively. Finally, results showed that synergistic effects induced by forming Cu2O/CuO heterojunction containing Cu-NPs co-cocatalyst greatly accelerate electron transfer and effectively retard the reduction of CuO by photo-generated electrons.

Synthesis of ZnO-nanorod-based materials for antibacterial, antifungal activities, DNA cleavage and efficient ultrasound-assisted dyes adsorption.

Undoped and Au-doped ZnO-nanorods were synthesized in the presence of ultrasound and loaded on activated carbon following characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmittance electron microscopy (TEM), UV-vis spectrophotometry and Fourier transform infrared spectroscopy (FTIR). The Au-doped ZnO-nanorod-loaded activated carbon (Au-ZnO-NRs-AC) was used for the simultaneous removal of methylene blue (MB) and auramine O (AO) from aqueous solutions. Central composite design (CCD) under response surface methodology (RSM) was applied to model and optimize the dyes removal versus adsorbent mass, pH, and initial dyes concentration and sonication time as well as to investigate the possible interaction between these variables. The optimum values of the initial MB and AO dyes concentration, adsorbent mass, pH and sonication time were found to be 12 and 10mgL-1, 0.0124g, 6.4, and 4min respectively. The rapid adsorption process at neutral pH using very small amount of the adsorbent makes it promising for the wastewater treatment applications. More than 99.5% of both dyes was removed with maximum adsorption capacities in binary-component system (107.5 and 95.7mgg-1 for MB and AO, respectively). The kinetics and isotherm studies showed that the second-order and Langmuir models apply for the kinetics and isotherm of the adsorption of MB and AO on the adsorbent used here. Moreover, the wastewater treatment by using an antibacterial/antifungal adsorbent makes the process much more valuable. Therefore, additional studies were performed which showed efficient antibacterial/antifungal activities and DNA cleavage of undoped and Au-doped ZnO nanorods as constituent of the adsorbent applied here.

Screening and optimization of highly effective ultrasound-assisted simultaneous adsorption of cationic dyes onto Mn-doped Fe3O4-nanoparticle-loaded activated carbon.

The ultrasound-assisted simultaneous adsorption of brilliant green (BG) and malachite green (MG) onto Mn-doped Fe3O4 nanoparticle-loaded activated carbon (Mn-Fe3O4-NP-AC) as a novel adsorbent was investigated and analyzed using first derivative spectrophotometry. The adsorbent was characterized using FT-IR, FE-SEM, EDX and XRD. Plackett-Burman design was applied to reduce the total number of experiments and to optimize the ultrasound-assisted simultaneous adsorption procedure, where pH, adsorbent mass and sonication time (among six tested variables) were identified as the most significant factors. The effects of significant variables were further evaluated by a central composite design under response surface methodology. The significance of independent variables and their interactions was investigated by means of the analysis of variance (ANOVA) within 95% confidence level together with Pareto chart. Using this statistical tool, the optimized ultrasound-assisted simultaneous removal of basic dyes was obtained at 7.0, 0.02g, 3min for pH, adsorbent mass, and ultrasonication time, respectively. The maximum values of BG and MG uptake under these experimental conditions were found to be 99.50 and 99.00%, respectively. The adsorption process was found to be followed by the Langmuir isotherm and pseudo-second order model using equilibrium and kinetic studies, respectively. According to Langmuir isotherm model, the maximum adsorption capacities of the adsorbent were obtained to be 101.215 and 87.566mgg-1 for MG and BG, respectively. The value of apparent energy of adsorption obtained from non-linear Dubinin-Radushkevich model (4.348 and 4.337kJmol-1 for MG and BG, respectively) suggested the physical adsorption of the dyes. The studies on the well regenerability of the adsorbent in addition to its high adsorption capacity make it promising for such adsorption applications.

Preparation of nanomaterials for the ultrasound-enhanced removal of Pb2+ ions and malachite green dye: Chemometric optimization and modeling.

Copper oxide nanoparticle-loaded activated carbon (CuO-NP-AC) was synthesized and characterized using different techniques such as FE-SEM, XRD and FT-IR. It was successfully applied for the ultrasound-assisted simultaneous removal of Pb2+ ions and malachite green (MG) dye in binary system from aqueous solution. The effect of important parameters was modeled and optimized by artificial neural network (ANN) and response surface methodology (RSM). Maximum simultaneous removal percentages (>99.0%) were found at 25mgL-1, 20mgL-1, 0.02g, 5min and 6.0 corresponding to initial Pb2+ concentration, initial MG concentration, CuO-NP-AC amount, ultrasonication time and pH, respectively. The precision of the equation obtained by RSM was confirmed by the analysis of variance and calculation of correlation coefficient relating the predicted and the experimental values of ultrasound-assisted simultaneous removal of the analytes. A good agreement between experimental and predicted values was observed. A feed-forward neural network with a topology optimized by response surface methodology was successfully applied for the prediction of ultrasound-assisted simultaneous removal of Pb2+ ions and MG dye in binary system by CuO-NPs-AC. The number of hidden neurons, MSE, R2, number of epochs and error histogram were chosen for ANN modeling. Then, Langmuir, Freundlich, Temkin and D-R isothermal models were applied for fitting the experimental data. It was found that the Langmuir model well describes the isotherm data with a maximum adsorption capacity of 98.328 and 87.719mgg-1 for Pb2+ and MG, respectively. Kinetic studies at optimum condition showed that maximum Pb2+ and MG adsorption is achieved within 5min of the start of most experiments. The combination of pseudo-second-order rate equation and intraparticle diffusion model was applicable to explain the experimental data of ultrasound-assisted simultaneous removal of Pb2+ and MG at optimum condition obtained from RSM.

Synthesis of magnetic γ-Fe2O3-based nanomaterial for ultrasonic assisted dyes adsorption: Modeling and optimization.

γ-Fe2O3 nanoparticles were synthesized and loaded on activated carbon. The prepared nanomaterial was characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transforms infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The γ-Fe2O3 nanoparticle-loaded activated carbon (γ-Fe2O3-NPs-AC) was used as novel adsorbent for the ultrasonic-assisted removal of methylene blue (MB) and malachite green (MG). Response surface methodology and artificial neural network were applied to model and optimize the adsorption of the MB and MG in their individual and binary solutions followed by the investigation on adsorption isotherm and kinetics. The individual effects of parameters such as pH, mass of adsorbent, ultrasonication time as well as MB and MG concentrations in addition to the effects of their possible interactions on the adsorption process were investigated. The numerical optimization revealed that the optimum adsorption (>99.5% for each dye) is obtained at 0.02g, 15mgL(-1), 4min and 7.0 corresponding to the adsorbent mass, each dye concentration, sonication time and pH, respectively. The Freundlich, Langmuir, Temkin and Dubinin-Radushkevich isotherms were studied. The Langmuir was found to be most applicable isotherm which predicted maximum monolayer adsorption capacities of 195.55 and 207.04mgg(-1) for the adsorption of MB and MG, respectively. The pseudo-second order model was found to be applicable for the adsorption kinetics. Blank experiments (without any adsorbent) were run to investigate the possible degradation of the dyes studied in presence of ultrasonication. No dyes degradation was observed.

Application of chitosan-citric acid nanoparticles for removal of chromium (VI).

In the present study, CS-CA nanoparticle was prepared for forming a new amide linkage, by grafting the amino groups of CS in the presence of carboxylic groups of CA that acts as cross-linking agent. The as-prepared CS-CA nanoparticle samples were characterized by use of dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, which showed that the cross-linking agent preserved during the chemical modifications. The adsorption capacity of the CS-CA nanoparticles for the removal of Cr (VI) in aqueous solution was studied. The adsorption equilibrium data taken at the optimized condition, i.e., 25 °C and pH of 3, were analyzed with the Langmuir, Freundlich and Redlich-Peterson isotherm models. The kinetics of Cr (VI) adsorption on CS-CA nanoparticles obtained at different initial concentrations were also analyzed using the pseudo-second-order model.

Simultaneous ultrasound-assisted ternary adsorption of dyes onto copper-doped zinc sulfide nanoparticles loaded on activated carbon: optimization by response surface methodology.

The simultaneous and competitive ultrasound-assisted removal of Auramine-O (AO), Erythrosine (Er) and Methylene Blue (MB) from aqueous solutions were rapidly performed onto copper-doped zinc sulfide nanoparticles loaded on activated carbon (ZnS:Cu-NP-AC). ZnS:Cu nanoparticles were studied by FESEM, XRD and TEM. First, the effect of pH was optimized in a one-at-a-time procedure. Then the dependency of dyes removal percentage in their ternary solution on the level and magnitude of variables such as sonication time, initial dyes concentrations and adsorbent dosage was fully investigated and optimized by central composite design (CCD) under response surface methodology (RSM) as well as by regarding desirability function (DF) as a good and general criterion. The good agreement found between experimental and predicted values supports and confirms the suitability of the present model to predict adsorption state. The applied ultrasound strongly enhanced mass transfer process and subsequently performance. Hence, a small amount of the adsorbent (0.04 g) was capable to remove high percentage of dyes, i.e. 100%, 99.6% and 100% for MB, AO and Er, respectively, in very short time (2.5 min). The experimental equilibrium data fitting to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models showed that the Langmuir model applies well for the evaluation and description of the actual behavior of adsorption. The small amount of proposed adsorbent (0.015 g) was applicable for successful removal of dyes (RE>99.0%) in short time (2.5 min) with high adsorption capacity in single component system (123.5 mg g(-1) for MB, 123 mg g(-1) for AO and 84.5 mg g(-1) for Er). Kinetics evaluation of experiments at various time intervals reveals that adsorption processes can be well predicated and fitted by pseudo-second-order and Elovich models.

Three-dimensional X-ray photoelectron tomography on the nanoscale: limits of data processing by principal component analysis.

In a previous article, we studied the influence of spectral noise on a new method for three-dimensional X-ray photoelectron spectroscopy (3D XPS) imaging, which is based on analysis of the XPS peak shape [Hajati, S., Tougaard, S., Walton, J. & Fairley, N. (2008). Surf Sci 602, 3064-3070]. Here, we study in more detail the influence of noise reduction by principal component analysis (PCA) on 3D XPS images of carbon contamination of a patterned oxidized silicon sample and on 3D XPS images of Ag covered by a nanoscale patterned octadiene layer. PCA is very efficient for noise reduction, and using only the three most significant PCA factors to reconstruct the spectra restores essentially all physical information in both the intensity and shape of the XPS spectra. The corresponding signal-to-noise improvement was estimated to be equivalent to a reduction by a factor of 200 in the required data acquisition time. A small additional amount of information is obtained by using up to five PCA factors, but due to the increased noise level, this information can only be extracted if the intensity of the start and end points for each spectrum are obtained as averages over several energy points.

XPS for non-destructive depth profiling and 3D imaging of surface nanostructures.

Depth profiling of nanostructures is of high importance both technologically and fundamentally. Therefore, many different methods have been developed for determination of the depth distribution of atoms, for example ion beam (e.g. O(2)(+) , Ar(+)) sputtering, low-damage C(60) cluster ion sputtering for depth profiling of organic materials, water droplet cluster ion beam depth profiling, ion-probing techniques (Rutherford backscattering spectroscopy (RBS), secondary-ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GDOES)), X-ray microanalysis using the electron probe variation technique combined with Monte Carlo calculations, angle-resolved XPS (ARXPS), and X-ray photoelectron spectroscopy (XPS) peak-shape analysis. Each of the depth profiling techniques has its own advantages and disadvantages. However, in many cases, non-destructive techniques are preferred; these include ARXPS and XPS peak-shape analysis. The former together with parallel factor analysis is suitable for giving an overall understanding of chemistry and morphology with depth. It works very well for flat surfaces but it fails for rough or nanostructured surfaces because of the shadowing effect. In the latter method shadowing effects can be avoided because only a single spectrum is used in the analysis and this may be taken at near normal emission angle. It is a rather robust means of determining atom depth distributions on the nanoscale both for large-area XPS analysis and for imaging. We critically discuss some of the techniques mentioned above and show that both ARXPS imaging and, particularly, XPS peak-shape analysis for 3D imaging of nanostructures are very promising techniques and open a gateway for visualizing nanostructures.