This study reports two new holder configurations that can be used in the diffusive gradients in thin films (DGT) technique, including a dual-mode holder and a new flat-type holder. The dual-mode holder can be assembled as a piston type, similar to the existing one for deployments in solution/water. It can also be assembled to form a hollow cylinder (open cavity) with 10 mm depth and 20 mm diameter, in which the soil paste is placed in contact with the exposed surface of the DGT unit at the bottom of the open cavity. Tests of the open cavity-type holder showed good agreement with the existing press-type holder in measurements of P, As, Cd and Pb in soils. However, the variability in measurements has been significantly reduced in the new holder configuration by 42%. This is due to the elimination of errors caused by manual pressing of the soil paste in the existing holder configuration. Moreover, the new flat-type holder used for deployment in sediments does not have the raised bottom edge design of the existing one, which allows its exposure surface to be on the same plane as the bottom of the holder. Tests of the new flat-type holder loaded with exposed sulfide binding gel showed that the penetration depths of dissolved sulfide and sulfide-enriched sands in sediments were only 33% and 20% of those obtained using the existing holder. The DGT measurements with the new holder resulted in low-concentration sulfide distribution at a much shallower depth (2.5 mm vs. 6 mm) by preventing the seepage of oxic overlying water into the sediment. The new holder usage also caused the disappearance of an abnormal sulfide-enriched slide in the top sediment layer, which likely resulted from the sulfide-enriched fecal pellets being pushed from the sediment surface into the top layer by the existing holder. These results demonstrate that the probe insertion-induced mobilization of dissolved and particulate substances has been reduced greatly with the new holder. Thus, the use of the new holder configurations can help to obtain much more accurate DGT measurements in soils and sediments. To the best of our knowledge, this is the first report describing a significant modification of the DGT holder configurations.

In this work, a novel electrochemical Hg²⁺ biosensor with high sensitivity and excellent reusability was presented. The sensor was based on tunable vertical single-walled carbon nanotubes (v-SWCNTs) and a target recycling strategy. A facile and scalable approach involving the conformational regulation of self-assembled monolayers was established for the fabrication of v-SWCNTs with tailored orientation and homogeneity. The obtained v-SWCNTs exhibited superior properties including a large specific area, high electrical conductivity, and excellent substrate binding strength, opening up a wide horizon for advanced electrochemical applications. Meanwhile, an efficient Hg²⁺ recycling strategy was designed using exonuclease III. In this strategy, a trace amount of Hg²⁺ triggered consecutive nicking reactions, and numerous report probes were released to bind with v-SWCNTs through π–π interactions. Based on the innovative design, an ultralow detection limit of 3 fM (S/N = 3), a wide linear range from 10 fM to 1 μM, high selectivity, and good reliability were achieved for a Hg²⁺ assay in water and serum samples using the prepared biosensor. Besides, due to the reversibility of π–π interactions, the stable v-SWCNT interface was regenerated for 50 consecutive measurements without obvious signal loss, making it a promising candidate for routine and efficient Hg²⁺ monitoring.