Low Detection Limit Research Articles

Computationally Optimized Graphene-Based Electrochemical Sensor with Enhanced Signal Stability for the Determination of the Antimicrobial Agent 9-aminoacridine

Abstract A hydrophobic aryl diazonium salt has been synthesized from 3,5-bis(trifluoromethyl)aniline and utilized to covalently modify graphene nanoplatelets and carbon nanotubes. The modified nanomaterials were applied on a screen-printed electrode/ion sensing membrane interface resulting in reduced potential drift to 100 μV/h compared to control sensors. Characterization was achieved through X-ray photoelectron spectroscopy. The electrode’s response was optimized using response surface methodology and then utilized for determination of 9-Aminoacridine (9-AA) in pharmaceutical gel dosage form and spiked human plasma without prior extraction steps. 9-AA is a fluorescent dye with antimicrobial activity that eradicates a range of microorganisms that can cause oral sores or broken skin and it has been recently used as anticancer among other uses as fluorescent dye and pH indicator. Accurate determination of 9-AA could help in adjusting dosages for each application. The optimized sensor was validated per IUPAC guidelines and obtained a wide linearity range from 1.0 × 10–7 M to 1.0 × 10–2 M, correlation coefficient of 0.9997, improved Nernstian slope 59.72, long term stability, and lower limit of detection (9.0 × 10–8 M). Furthermore, Analytical Eco-scale and AGREE methods were utilized to evaluate the presented method's greenness.

Laser-induced the enhancement of Raman scattering performance in WO3-x/Ag composite films

Non-stoichiometric tungsten oxide (WO3-x) has controllable defects, high charge density, and good synergy with other materials to exhibit good surface-enhanced Raman scattering (SERS) properties. Its heterojunction structure provides an opportunity to develop high-quality and low-cost SERS substrates. This study obtained WO3-x/Ag composite thin films were obtained by Nd: YAG fiber pulsed laser modification at ambient conditions. The effects of interactions between heterojunctions and laser modification on the samples’ morphology, composition, and optical properties were investigated. The absorption peaks exhibited a red shift by varying the laser scan speeds, and the SERS properties of the sample were evaluated by methylene blue (MB) dye. The results show that the laser-modified WO3-x/Ag films have good stability as SERS substrates. The characteristic peaks of MB can still be detected after 90 days in the air. The WO3-x/Ag films also have good homogeneity and a low detection limit, with a limit of detection (LOD) as low as 10−7 M, and an enhancement factor as high as 1.34 × 104. The simulated results by the finite difference in time domain (FDTD) showed substantial agreement with those of the experimental ones.

Enhanced sensitivity in tobramycin monitoring using a surfactant-aligned liquid crystal aptasensor with a ternary hybrid aptamer

Determining pharmaceutical residues in foodstuffs is of great importance worldwide. The improper use of tobramycin (TOB) with abroad spectrum antibacterial activity results in its accumulation in the food chain and human body. Given its detrimental effects on human health, the careful surveillance of TOB concentrations is essential to ensure food safety. Presented here is a highly sensitive aptasensing array designed to measure the TOB concentration by disrupting the alignment of liquid crystal (LC) molecules induced by surfactants. For the first time, a ternary hybrid of the aptamer strands was incorporated onto the surfactant-designed LC-aqueous interface instead of a single strand of aptamer, causing a significant disruption in the customary orientation of LCs. This changed the brightness quantity from 35.06 to 69.54, due to higher interaction with the positively charged section of the surfactant than that for one aptamer strand. The presence of TOB caused the ternary aptamer hybrid to break apart by creating the complex between the aptamer and TOB, separating the aptamer strands from the LC-aqueous interface. Subsequently, the TOB presence was specified by inducing a color change in the polarized vision of the aptasensor platform, resulting in a shift from colorful to murky. The aptasensor could monitor TOB in the linear concentration range of 1 fM-10 nM, with an impressively low detection limit of 0.217 fM. With the capability to determine TOB in beef, chicken egg, and low-fat milk, the LC-decorated aptasensor is proficient in food quality control. The aptasensor possesses characteristics such as simplicity, high sensitivity, ease of use, and affordability. As a result, it has the potential to be marketed as a portable testing kit that is convenient and cost-effective.

Synthesis of Thioglycolic Acid-Modified Molybdenum Disulfide Nanosheets for Electrochemical Sensing and Its Application in Molnupiravir Detection

Abstract In the modern world, population growth, industrialization, and lifestyle changes have led to a rise in existing and new diseases, increasing global drug consumption. Proper pharmaceutical dosage is vital since drugs are only effective within specific concentration ranges. Therefore, developing reliable analytical methods for drug analysis in pharmaceuticals and biological samples is essential. Electroanalytical methods are particularly advantageous due to their low cost, ease of use, and rapid response. This study introduces a highly sensitive electrochemical sensor based on thioglycolic acid (TA)-decorated metallic phase molybdenum disulfide (MP-MoS2) nanosheets for the selective detection of molnupiravir (MOL), an antiviral drug used in Covid-19 treatment. The TA@MP-MoS2 nanomaterial was characterized using FTIR, TEM, and EIS. Screen-printed carbon electrodes (SPCE) were modified with TA@MP-MoS2 nanosheets to evaluate their electro-chemical and catalytic behaviours towards MOL by cyclic voltammetry (CV) and square wave voltammetry (SWV). The sensor displayed a well-defined electro-oxidation signal for MOL at 0.534 V, with the linear responses in two concentration ranges: 0.50 – 3.40 µM and 3.40 – 9.55 µM, and a low detection limit of 22.6 nM. The proposed design that has promising results could be an alternative strategy to fabricate the sensitive sensor for the detection of antiviral agents in real samples

Manganese-arginine nanozymes as oxidase mimics for smartphone-based intelligent detection of 4'-O-methylpyridoxine.

Byself-assembly of MnCl2 and arginine under alkaline conditions, ultra-small MnArg nanoparticles were successfully constructedas oxidase (OXD) mimics for intelligent detection of the Ginkgo toxin 4'-O-methylpyridoxal (MPN). The obtained MnArg nanozymes possessed excellent OXD-like activity and thermal stability. Based on the inhibitory effect of MPN for the catalytic activity of MnArg, this system wasutilized for the colorimetric sensing of MPN with a low limit of detection (LOD) of 2.16µgmL-1. Thedetection system exhibited good selectivity against other potential interferents. FTIR data showed that the presence of MPN binds with MnArg and shields the active sites, thereby interfering with the oxidase-like activity. Combined with a smartphone and the ColorMax software, this nanozyme-based intelligent detection platform could effectively detect MPN with a LOD of 2.1µgmL-1. Our MnArg nanozyme-based system wasapplied to detect real ginkgo nut samples with recoveries of 92.4-108.7%, and the relative standard deviations were less than 0.7%. This work may promote the development of novel nanozymes and expand their applications in the field of food safety detection.

Observation of Body‐Centered‐Cubic Cu Nanocluster with Partial Cu(0) Character

The structure of nanoparticles is a key determinant of their material properties. The synthesis of non‐face‐centered‐cubic (FCC) Cu nanoclusters (NCs) with Cu(0) character is still challenging due to their instability. Herein, a Cu(0)‐containing Cu NC is first reported to contain a metallic framework of 23 Cu atoms with a body‐centered‐cubic Cu@Cu8 core, stabilized by 6 triphenylphosphine (TPP) and 18 4‐methylbenzenethiolate ligands, as determined by single‐crystal X‐ray crystallography. The observed structure stands in stark contrast to the FCC and other structures reported for Cu NCs. Moreover, this newly formed NC could react with Au+ ion with controlled concentration, rapidly yielding another identifiable and bright red‐emitting AuCu14 cluster upon irradiation. Based on this structural conversion, a new “turn‐on” type of photoluminescent probe can be developed for the detection of Au+ ion with an ultrafast response time (30 s) at a low detection limit (0.13 ppm). This work provides a new way of understanding the growth of metal clusters and exploring their applications in luminescent sensors.

Paper-Based DNA Biosensor for Rapid and Selective Detection of miR-21

Cancer is the second leading cause of death globally, with 9.7 million fatalities in 2022. While routine screenings are vital for early detection, healthcare disparities persist, highlighting the need for equitable solutions. Recent advancements in cancer biomarker identification, particularly microRNAs (miRs), have improved early detection. MiR-21 is notably overexpressed in various cancers and can be a valuable diagnostic tool. Traditional detection methods, though accurate, are costly and complex, limiting their use in resource-limited settings. Paper-based electrochemical biosensors offer a promising alternative, providing cost-effective, sensitive, and rapid diagnostics suitable for point-of-care use. This study introduces an innovative electrochemical paper-based biosensor that leverages gold inkjet printing for the quantitative detection of miR-21. The biosensor, aimed at developing cost-effective point-of-care devices for low-resource settings, uses thiolated self-assembled monolayers to immobilize single-stranded DNA-21 (ssDNA-21) on electrodeposited gold nanoparticles (AuNPs) on the printed gold surface, facilitating specific miR-21 capture. The hybridization of ssDNA-21 with miR-21 increases the anionic barrier density, impeding electron transfer from the redox probe and resulting in a current suppression that correlates with miR-21 concentration. The biosensor exhibited a linear detection range from 1 fM to 1 nM miR-21 with a sensitivity of 7.69 fM µA−1 cm2 and a rapid response time (15 min). With a low detection limit of 0.35 fM miR-21 in serum, the biosensor also demonstrates excellent selectivity against interferent species. This study introduces an electrochemical paper-based biosensor that uses gold inkjet printing to precisely detect miR-21, a key biomarker overexpressed in various cancers. This innovative device highlights the potential for cost-effective, accessible cancer diagnostics in underserved areas.

Plasmonic Coacervate as a Droplet-Based SERS Platform for Rapid Enrichment and Microanalysis of Hydrophobic Payloads.

A novel and simple coacervate microdroplet-based detection platform for the quantification of trace hydrophobic analytes is presented. Herein, taking advantage of the effective encapsulation and enrichment performance of the condensed coacervates, plasmonic metallic silver nanoparticles (AgNPs) and target hydrophobic analytes are simultaneously concentrated into a single microdroplet. The coencapsulation of AgNPs within coacervates promotes the formation of aggregates with a lot of "hot spots" for surface-enhanced Raman scattering (SERS) enhancement, facilitating the sensitive analysis of hydrophobic analytes by SERS technology. Such plasmonic coacervates are easily prepared and exhibit good reproducibility and signal uniformity. Optimized SERS performance by modulating the volume of encapsulated AgNPs enables quantitative determination of hydrophobic analytes of Nile Red, chlorpyrifos, benzo[e]pyrene, 20 and 50 nm polystyrene nanoplastics with low detection limits of 10-12 M, 10-9 M, 10-10 M, 0.05 ppb, and 0.5 ppb, and an approximately linear correlation between SERS signals and the analytical concentrations. This study opens a new convenient SERS platform for the ultrasensitive detection of hydrophobic hazardous substances, potentially becoming a rapid analysis method for extensive applications ranging from food safety to environment monitoring.

Determination of naringin and neohesperidin in "Quzhiqiao" (Immature fruit of Citrus paradisi 'Changshan Huyou') using graphene-based molecularly imprinted technology

A sensitive and selective molecularly imprinted polymer-graphene oxide (MIP@GO) electrochemical sensor was fabricated for the determination of naringin and neohesperidin in "Quzhiqiao" (immature fruit of Citrus paradisi 'Changshan Huyou'). The MIP@GO was prepared by electropolymerization using naringin and neohesperidin as templates. Under optimized conditions, the sensor exhibited linear ranges of 0.1–50 μM for naringin and 0.2–60 μM for neohesperidin, with low detection limits of 0.03 μM and 0.05 μM, respectively. The imprinting factors for naringin and neohesperidin were 3.8 and 2.5, respectively. The sensor demonstrated excellent selectivity, reproducibility (RSD < 3.6 %), stability (>94.5 % retention after 30 days), and reusability (>92.8 % retention after 10 cycles). The MIP@GO sensor was successfully applied to Fructus aurantii samples, with recoveries ranging from 95.5 % to 104.2 %. This work presents a rapid, cost-effective, and highly sensitive approach for the quality control of Quzhiqiao and related citrus products.

All‐Paper‐Based, Flexible, and Bio‐Degradable Pressure Sensor with High Moisture Tolerance and Breathability Through Conformally Surface Coating

AbstractHighlighted with bio‐degradability, paper‐based flexible pressure sensors receive significant attention in the field of wearable devices for a sustainable future. However, it remains a challenge to possess considerable sensing performance in high humidity and underwater environments, because its structure rapidly breaks down after the hydrophilic cellulose absorbs water. In this study, a facile chemical vapor deposition method is employed to conformally coat a thin hydrophobic layer onto the cellulose fibers, resulting in an encapsulating paper with high moisture tolerance. The well‐maintained porous structure reserves the superior breathability of the paper. A micro‐convex‐structured sensor layer impregnated with MXene serves as the sensing layer. As a result, an all‐paper‐based pressure sensor with high moisture tolerance and breathability is fabricated. This sensor features a broad sensing range (0–60 kPa), acceptable sensitivities (39.58 kPa−1 (0–1.01 kPa), 11.95 kPa−1 (1.01–60 kPa)), a low detection limit of ≈2.8 Pa, response and recovery time (93 and 69 ms), reliable hydrophobic breathability, and excellent repeatability (10 000 cycles). Moreover, this sensor can be safely worn on human skin and can monitor physiological signals in real‐time in different environments (including air, humid environments, and even underwater), providing a reliable, economical, and environmentally friendly solution for wearable technology.

An Aggregation-Induced Emissive Platinum(II) Metallacycle as the Energy Donor of Rhodols for Ratiometric Detection of Hydrazine.

Industry-produced hydrazine (N2H4) is released into the environment, posing a major risk to human health and the ecosystem. Therefore, it is imperative to develop an effective and convenient method for the detection of N2H4. Herein, artificial light-harvesting systems (ALHSs) for N2H4 detection were constructed by applying an aggregation-induced emission-active platinum(II) metallacycle (TPEMc) as the energy donor and rhodols (P1, P2, and P3) as the energy acceptors. The ratiometric fluorescence probes based on ALHSs for N2H4 showed obvious signal amplification and lower limits of detection compared to those of rhodols (P1, P2, P3) alone. The TPEMc-rhodols systems clearly demonstrated a noticeable increase in fluorescence intensity at 550 nm and an obvious fluorescent color shift from cyan to yellow in the presence of N2H4. Fascinatingly, N2H4 could be visually and quantitatively detected in water by the TPEMc-rhodol systems paired with smartphone RGB analysis. Therefore, the combination of platinum(II) metallacycle with rhodols is a promising strategy for simple, sensitive, and visual detection of N2H4.

Ultrasensitive Rapid Antigen Test by Geometric Lateral Flow Assays and Highly Doped Upconversion Nanoparticles.

The paper-based lateral flow assay (LFA) testing strips are currently the most widely used for point-of-care testing (POCT), valued for their rapid result turnaround times in a few minutes. However, their sensitivity has been limited. Upconversion nanoparticles (UCNPs), especially highly doped ones, have emerged as promising luminescent reporters to enhance the LFA sensitivity. These UCNPs exhibit a nonlinear enhancement in luminescence with excitation power density, necessitating higher power densities for higher brightness. In this study, we utilized a geometric paper strip design to minimize the immune reaction area and maximize the excitation power density, enabling ultrasensitive detection of the SARS-CoV-2 nucleoprotein antigen. This design also slowed the antigen flow on the paper strip, extending the reaction time between antigen and antibody, thereby enhancing the efficiency of the immune reaction. Through this design, our approach achieved over a 100-fold enhancement in the limit of detection (LOD) compared with the widely used LFAs, based on gold colloidal nanoparticles and europium nanoparticles. This innovation expands the scope of LFA applications that require a low LOD.

A Low-Cost, Portable, Multi-Cancer Screening Device Based on a Ratio Fluorometry and Signal Correlation Technique

The autofluorescence of erythrocyte porphyrins has emerged as a potential method for multi-cancer early detection (MCED). With this method’s dependence on research-grade spectrofluorometers, significant improvements in instrumentation are necessary to translate its potential into clinical practice, as with any promising medical technology. To fill this gap, in this paper, we present an automated ratio porphyrin analyzer for cancer screening (ARPA-CS), a low-cost, portable, and automated instrument for MCED via the ratio fluorometry of porphyrins. The ARPA-CS aims to facilitate cancer screening in an inexpensive, rapid, non-invasive, and reasonably accurate manner for use in primary clinics or at point of care. To accomplish this, the ARPA-CS uses an ultraviolet-excited optical apparatus for ratio fluorometry that features two photodetectors for detection at 590 and 630 nm. Additionally, it incorporates a synchronous detector for the precision measurement of signals based on the Walsh-ordered Walsh–Hadamard transform (WHT)w and circular shift. To estimate its single-photodetector capability, we established a linear calibration curve for the ARBA-CS exceeding four orders of magnitude with a linearity of up to 0.992 and a low detection limit of 0.296 µg/mL for riboflavin. The ARPA-CS also exhibited excellent repeatability (0.21%) and stability (0.60%). Moreover, the ratio fluorometry of three serially diluted standard solutions of riboflavin yielded a ratio of 0.4, which agrees with that expected based on the known emission spectra of riboflavin. Additionally, the ratio fluorometry of the porphyrin solution yielded a ratio of 49.82, which was ascribed to the predominant concentration of protoporphyrin IX in the brown eggshells, as confirmed in several studies. This study validates this instrument for the ratio fluorometry of porphyrins as a biomarker for MCED. Nevertheless, large and well-designed clinical trials are necessary to further elaborate more on this matter.

Impregnation of two-dimensional manganese dioxide nanosheets with 5-carboxyfluorescein as an immunoassay platform for sensitive detection of cardiac troponin T.

Anovel immunoassay platform is presentedutilizing a cardiac troponin T antibody (Ab-cTnT) labelled with 5-carboxyfluorescein (5-FAM) integrated into a two-dimensional (2D) manganese dioxide nanosheet (MnO2 NS) matrix. This strategy enables a turn-on response towards cTnT antigen within a mere 10-min incubation period, boasting an impressive lower detection limit of 0.038ng/mL. Crucially, our probe demonstrates exceptional selectivity amidst the presence of coexisting biomolecules and ions, ensuring precise detection of cTnT. Moreover, the developed platform showcases promising utility in sensing cTnT from spiked human serum samples, yielding satisfactory recovery percentages ranging from 82 to 105%. Additionally, we introduce and easy-to-use and cost-effective test strip for point-of-care detection of cTnT, further enhancing accessibility to critical cardiovascular diagnostics.

An improved amperometric cholesterol biosensor based on cholesterol oxidase nanostructures for pre-diagnosis of myocardial infarction

Cholesterol plays a pivotal role in human health, serving as a crucial biomarker for cardiovascular diseases, including myocardial infarction. This study presents the development of an innovative amperometric cholesterol biosensor that enhances the detection and quantification of cholesterol levels in serum. The biosensor integrates cholesterol oxidase (ChOx) nanoparticles with a modified electrode, leveraging the unique properties of platinum nanoparticles (PtNPs) and graphene nanosheets (GNs) to improve sensitivity and stability. The synthesis of PtNPs was achieved using Camellia sinensis extract, while graphene oxide was reduced to form GNs. At 2.39 mg/mL or above is deemed a biomarker for cardiovascular disorders, peripheral artery disease, heart attack, diabetes mellitus, strokes, and hypertension. The monitoring of serum cholesterol level is therefore very significant. In the present study, an innovative amperometric cholesterol biosensor was constructed by immobilizing nanoparticles of cholesterol oxidase onto a pencil graphite (PG) electrode modified with graphene nanosheets (GNs), platinum nanoparticles (PtNPs), and chitosan (CHIT). At various stages of construction, the modified electrode was characterized by employing electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The biosensor responded best when run at 0.14Vs-1 at optimal pH and temperature of 8.0 and 35°C respectively. The biosensor has a wide linear range (0.1mg/mL-7.5 mg/mL), with great sensitivity (0.89 mA cm−1mgmL−1) and a low limit of detection (0.97 mg/mL). This research not only contributes to the field of biosensing but also offers a promising tool for the early diagnosis of cholesterol-related health issues, paving the way for enhanced cardiovascular disease management.

Construction of a In2O3/ultrathin g-C3N4 S-scheme heterojunction for sensitive photoelectrochemical aptasensing of diazinon

A single semiconductor-based photoelectrochemical (PEC) aptasensor usually faces a challenge of low sensitivity due to poor solar energy utilization and a high photogenerated carrier recombination rate. Herein, an ultra-thin carbon nitride nanosheet-coated In2O3 (In2O3/CNS) S-type heterojunction-based PEC aptasensor has been established to achieve highly sensitive detection of diazinon (DZN) pesticide in water environment. Construction of S-type heterojunction induces a band shift and an electric field effect, enhancing light utilization and accelerating directional transmission of carriers, leading to outstanding PEC performance. The creation of internal electric field at interface ensures stable carrier transport. Additionally, ultrathin CNS structure can effectively shorten the transport path of carriers. The close coating of In2O3 and CNS promotes the transfer of charge. The synergistic effects amplify the sensor’s response, ultimately enabling the effective detection of DZN residue over a wide detection range (0.98 ∼ 980.0 pg mL−1), a low detection limit (0.33 pg mL−1, S/N = 3) and excellent accuracy in practical application (RSD < 5 %). This work provides a reference for the construction of a new S-type heterojunction-based PEC sensor.

High‐Performance Flexible Gas Sensor Using Natural Rubber/MXene Composite for Selective and Stable VOC Detection

AbstractFlexible gas sensors are gaining interest for real‐time volatile gas monitoring. A natural rubber (NR)/MXene nanocomposite sensor is developed. Among the six selected target volatile gases, the composite sensor exhibited a strong response value (82% toward 100 ppm NH3) with the fastest response/recovery time (12.3 s/15.5 s) to NH3. The sensitivity showed a clear dependence of gases, suggesting a good selectivity to varying gases. Ti3C2Tx MXene gas sensors exhibited a very low limit of detection of 50–100 ppb for volatile organic compounds (VOCs) at room temperature. In addition, the NR/MXene sensor allows detection of the mixture of ammonia (NH3), dimethyl sulfoxide (DMSO), and acetone (C3H6O) and it shows good response depending on the total concentration of VOC gases. Furthermore, the flexible nanocomposite sensor exhibits stable sensing performance at different bending states (0‐120°) and shows 20‐day atmospheric stability. This sensor's ability extends to alcohol breath analysis, useful for drunk driving detection. This work paves the way to the possibility of using robust MXene‐based toward practical realization of electronic devices.

8408 Comparison of Free Thyroxine (fT4) Reference Ranges in Pregnancy: Evaluanting a Novel Equilibrium Dialysis Coupled with Liquid Cromatography Tandem Mass Spectrometry Analytical Method Versus a Standard Routine Immunoassay

Abstract Disclosure: R.M. Biscolla: Employee; Self; Fleury Medicina e Saude. A. Lebkuchen: Employee; Self; Fleury Medicina e Saude. K.H. Cardozo: Employee; Self; Fleury Medicina e Saude. V.M. Carvalho: Employee; Self; Fleury Medicina e Saude. M.T. Justa: Employee; Self; Fleury Medicina e Saude. J.G. Vieira: Owner/Co-Owner; Self; Fleury Medicina e Saude. M.I. Chiamolera: Employee; Self; Fleury Medicina e Saude. There is a difficulty in assessing thyroid function during the gestational period and one of the most important reasons is the changes in TBG during pregnancy, resulting from the increase in estrogen, lead to interference in the dosages of free thyroxine (fT4) measured by commercial competitive immunoassays, posing limitations on the accuracy and sensitivity of existing assessment methods. Therefore, it is necessary to establish specific reference values for each trimester and for the different methods, so the analysis of fT4 results could be more confidently used in clinical practice.Objective: This study aimed to describe a new direct method for measuring free thyroxine (fT4) utilizing equilibrium dialysis (ED) coupled with liquid chromatography tandem mass spectrometry (LC–MS/MS). Additionally, the performance of this method was compared to a commercial immunoassay, and trimester-specific normal reference ranges for fT4 in pregnancy were determined. Methods: We developed a novel ED LC–MS/MS analytical method employing 96-well dialysis plates for measuring fT4 that demonstrated an adequate sensitivity, precision, and linearity. A total of 291 samples from pregnant women were analyzed, the gestational trimester was determined using ultrasound. Additionally, serum fT4 was assessed using an immunoassay with Beckman Coulter kits to compare the two methods. Results: The lower limit of detection (LLOQ), and upper limit of detection (ULOQ) of the new method were respectively calculated to be 0.4 ng/dL and 20.8 ng/dL. The comparison between the two methods showed median FT4 concentrations of 0.7 ng/dL (range, 0.5–1.1 ng/dL) for the immunoassay and 1.1 ng/dL (0.6–2.1 ng/dL) for the ED LC–MS/MS assay (paired t test, p &amp;lt; 0.0001). A significant correlation between methods was observed (Spearman’s r= 0.4898, p &amp;lt; 0.0001). fT4 reference values for ED LC–MS/MS (2.5–97.5 percentiles) were 0.9–1.9 ng/dL, 0.7–1.4 ng/dL, and 0.7–1.5 ng/dL for the first, second, and third trimesters, respectively, whereas median TSH levels were 1.7 mIU/L (0.05–4.0 mIU/L), 1.7 mIU/L (0.44–3.7 mIU/L), and 1.9 mIU/L (0.28–3.5 mIU/L) for the first, second, and third trimesters, respectively.Conclusions: The study with a recent developed LC-MS/MS fT4 method pointed to the differences with an immunoassay method and underscores the importance of establishing trimester- and method- specific normal reference ranges in pregnancy. Presentation: 6/3/2024

7692 Morning Cortisol Levels In Patients With Established Primary Adrenal Insufficiency

Abstract Disclosure: A. Prete: Research Investigator; Self; Diurnal. V. Theiler-Schwetz: Research Investigator; Self; Diurnal. W. Arlt: Research Investigator; Self; Diurnal. I.O. Chifu: Research Investigator; Self; Diurnal. B. Harbeck: Research Investigator; Self; Diurnal. C. Napier: Research Investigator; Self; Diurnal. J.D. Newell-Price: Research Investigator; Self; Diurnal. A. Rees: Research Investigator; Self; Diurnal. N. Reisch: Research Investigator; Self; Diurnal. G.K. Stalla: Research Investigator; Self; Diurnal. N. Aslam: Employee; Self; Diurnal. H. Coope: Employee; Self; Diurnal. K. Maltby: Employee; Self; Diurnal. J. Porter: Employee; Self; Diurnal. J. Quirke: Employee; Self; Diurnal. R.J. Ross: Consulting Fee; Self; Diurnal. Background: Primary adrenal insufficiency (PAI) is rare: prevalence ∼100-140/million and incidence 4:1 000 000/year in Western societies [1]. The diagnosis of PAI is suggested by an early-morning cortisol &amp;lt;140 nmol/L (5 µg/dL) [1]. The commonest cause in adults is autoimmunity (∼90% in Western countries) and it is generally considered progressive once the diagnosis is made, although it has been reported that residual cortisol secretion is present in ∼30% of patients 2. We have developed a modified-release formulation of hydrocortisone to replace the physiological cortisol circadian rhythm and are undertaking a Double-Blind, Double-Dummy, Two-Way Cross-Over, Randomised, Phase II Study of Modified-Release Hydrocortisones: Chronocort® Versus Plenadren® in PAI. During recruitment, we were surprised by the number of patients who were ineligible as they had detectable morning cortisol levels. Methods: Main inclusion criteria: Participants with known PAI on stable glucocorticoid replacement therapy and an early morning pre-dose cortisol &amp;lt;50 nmol/L (1.8 µg/dl). Baseline serum cortisol was taken at ∼0700h and measured in a central laboratory by ADVIA Centaur® immunoassay with the lower limit of detection &amp;lt;14nmol/l (&amp;lt;0.5 µg/dL). Results: 86 patients with PAI (autoimmune aetiology in 71), median age 52 years (range 20-73), 60 female, were screened in 8 centres in UK and Germany. 18 (21%) patients were excluded from the study based on morning cortisol &amp;gt;50 nmol/L (1.8 µg/dL), and of those 68 patients who qualified on the main inclusion criteria 51 (59% of screened) had a cortisol &amp;lt;14 nmol/L (&amp;lt;0.5 µg/dL). Of the 18 patients (autoimmune aetiology in 10) excluded based on their morning cortisol level, 9 (50%) were female and 11 (13% of screened), had morning cortisol ≥140 nmol/L (5.0 µ/dL). 12 patients with morning cortisol of &amp;gt;50nmol/L (1.8 µ/dL) were retested and only 2 then qualified; their initial morning cortisol levels were 70 and 51 nmol/L. In patients retested the median difference between retest and the initial sample was 13 nmol/L (range 1-421 nmol/L). Conclusions: In patients with an established diagnosis of PAI, the majority had undetectable morning cortisol, but cortisol was detectable in 41% of patients and above 140 nmol/L in 13% confirming previous publications 2. Retesting patients with a cortisol &amp;gt;50nmol/L showed very similar results suggesting that the detectable cortisol was not an artefact and likely due to background cortisol secretion. 1. Bornstein SR, et al. J Clin Endocrinol Metab 2016;101:364-89.2.Pearce SHS, et al. European Journal of Endocrinology (2021) 184, R61–R67 Presentation: 6/1/2024

Cu2O/Cu-MOF/Fe-MIL-88B with peroxidase activity for intelligent detection of p-aminophenol and barbituric acid and virtual reality display for detection mechanism

The bimetallic organic framework nanoenzyme Cu2O/Cu-MOF/Fe-MIL-88B is synthesized by the solvothermal method. The characterizations of transition electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry prove that the amounts of oxygen vacancies are existed on the surface of Cu2O/Cu-MOF/Fe-MIL-88B and stronger electron transfer is the key factor for free radical •OH and O2·- production, thus exhibiting excellent peroxidase activity of Cu2O/Cu-MOF/Fe-MIL-88B. On the basis of the excellent peroxidase activity, versatile colourimetric and intelligent detection platforms for p-aminophenol and barbituric acid are successfully constructed on site and timely. The linear ranges of p-aminophenol and barbituric acid are 25–75 μM and 5–45 μM, and the lowest limits of detection (LOD) are 0.51 μM and 0.46 μM, severally. Moreover, the mechanisms for detecting p-aminophenol and barbituric acid were displayed by virtual reality technology. Therefore, the colourimetric and intelligent sensor of p-aminophenol and barbituric acid based on the peroxidase of Cu2O/Cu-MOF/Fe-MIL-88B have a hopeful prospect in the field of biomedicine.