Signal Enhancements in Plasmon Assisted Fluorescence Ratiometric Imaging Optodes

The objective of this study was to benchmark the different signal enhancements found in a recently exploited fluorescence ratiometric optode design used for nano-molar imaging of ammonium and ammonia. The sensing scheme of these optodes are based on a mediated transfer of the analyte together with a fluorescent dye in a two-phase system consisting of a gold nanoparticle (GNP) doped ether (organic phase), emulsified in a hydrogel (hydrous phase). The coextraction of the ion dye pair causes changes in fluorescence in relation to the analyte concentration. Performances of optodes with and without GNPs using the gradually improved instrumentation and signal processing were evaluated and normalized to be comparable. Signal to noise was enhanced due to signal processing based on ensemble averaging (1.7× - 3.2×), CCD sensitivity (2×), and plasmon assisted fluorescence (10× - 100×), which altogether with the ratiometric treatment of the fluorescence contributed to the great sensitivity for ammonium and ammonia. The study shows that GNP doped sensors are relatively more sensitive to matrix effects but if they are isolated by a protective layer they will dramatically increase in sensitivity. Proper isolation of the active chemical components from the matrix will make the sensor design one of the most powerful and versatile concepts for chemical imaging and single point detection in complex environments as the optodes likely can be constructed for most ions that have selective ionophores.

Optical Chemical Sensor for Screening Cadmium (II) in Natural Waters

Membrane based optical chemical sensor (optode) for Cd(II) was developed by the immobilization of a dye 1-(2-Pyridylazo)-2-Napthol (PAN) in the Tri-(2-Ethylhexyl) Phosphate (TEHP) plasticized Cellulose Triacetate (CTA) matrix. Various combinations of PAN immobilized in the cellulose triacetate CTA and Polystyrene (PS) matrices plasticized with Tri-(2-Ethylhexyl) Phosphate TEHP, 2-Nitrophenyl Octyl Ether (NPOE) and Dioctyl Phthalate (DOP) were studied to arrive a suitable composition and found that the optode does not require any extractant to produce a distinct colour change on complexation with Cd(II). On sorption of Cd(II) in the optode matrix, PAN changes color of the optode from golden yellow to violet red having a maximum absorbance (lmax = 553 nm) within 150 min of total equilibration time at pH = 7.5. The optode developed in the present work was studied for its analytical application for Cd(II) in the aqueous samples by spectrophotometry and as well as Flame Atomic Absorption Spectrophotometry (FAAS). This preconcentrated optode showed a linear response by UV-visible spectrophotometry at λmax = 553 nm over a concentration range of 10 ng/mL–1 to 500 ng/mL–1 of Cd(II) ions. Where as the aqueous solutions was also subjected to FAAS before and after equilibration of the optode and found to be linear in the concentration range of 250 ng/mL–1 to 5000 ng/mL–1 of Cd(II) ions. The optode found to be reversible and can be desorbed by equilibrating it with 0.01 mol/L–1 HNO3. The applicability of the developed optode in real samples was studied by determining cadmium in the natural waters spiked with a known amount of Cd(II) ions.

Phosphorus removal from sediments by Potamogeton crispus:New high-resolution in-situ evidence for rhizosphere assimilation and oxidization-induced retention

Macrophytes are usually chosen for phytoremediation tools to remove P in eutrophic aquatic ecosystems,but the lack of test methods hinders the understanding of removal mechanism and application.In this study,we used the novel technologies combined of Diffusive gradients in thin films(DGT),Planar optode(PO),and Non-invasive micro-test technology(NMT)to explore P dynamics in water-sediment continuum and rhizosphere of Potamogeton crispus over time.Results of the high-resolution in situ measurement showed that labile P(LPDGT)fluxes at the surficial sediment significantly decreased from approximate 120,140,and 200 pg/(cm^(2)·sec)via 30 days incubation period to 17,40,and 56 pg/(cm2•sec)via that of 15 days.Obvious synchronous increase of LPDGT was not detected in overlying water,suggesting the intense assimilation of dissolve reactive P via root over time.PO measurement indicated that O_(2)concentration around the rhizosphere remarkably increased and radially diffused into deeper sediment until 100%saturation along with the root stretch downwards.NMT detection of roots showed the obvious O_(2)inflow into root tissue with the uppermost flux of 30 pmol/(cm2•sec)from surroundings via aerenchyma on different treatment conditions.Different from previous reports,gradually saturating O_(2)concentrations around the rhizosphere was principally driven by O_(2)penetration through interspace attributing to root stretch downward rather than root O_(2)leakage.Increased O_(2)concentrations in deep sediment over time finally induced the oxidization of labile Fe(II)into Fe(III)bound P and local P immobilization.

Seasonal dynamics of iron and phosphorus in reservoir sediments in Eucalyptus plantation region

Background:Iron(Fe)and phosphorus(P)dynamics in sediments have direct and indirect impacts on water quality.However,the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear.This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode,the ZrO-Chelex DGT,and the DIFS model.Results:Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments(X2)compared to sediments without Eucalyptus species(X1).The mean concentration of labile P and Fe decreased by 25%and 42%from X1 to X2.The decrement was insignificant(p=0.20)in the surface sediment concentration for labile P.The significant disparity for DGT-Fe(Fe^(2+))(p=0.03)observed in the surface sediments could be attributed to the Eucalyptus species’elevated organic matter(tannins)concentration at X2,which reacted and consumed labile Fe.For both regions,the maximum concentration of labile P and Fe occurred in November(autumn).The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November.Low concentration of labile P and Fe was observed in December(winter)due to the adsorption of Fe/Mn oxides.The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship(r>0.8,p<0.01)in both regions.The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe.The fluxes of labile P and Fe in both regions were substantially higher(p<0.05)in the summer(anoxic period)than winter(aerobic period),indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe.From the DIFS model,the replenishment ability of reactive P was higher during the anoxic period(R=0.7,k_(1)=79.4 day^(-1),k_(-1)=0.2 day^(-1))than the aerobic period(R=0.4,k_(1)=14.2 day^(-1),k_(-1)=0.1 day^(-1)),suggesting that oxygen inhibited the efflux of P in the sediments.Conclusion:Our results indicated that hypoxia,Eucalyptus species(organic matter(tannins)),and redox conditions influenced the seasonal mobility of sediment labile P and Fe.Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and,moreover,serves as a reference for developing future studies on Eucalyptus-dominated sediments.