Guanidinium-Functionalized Polymer Dielectrics for Triboelectric Bacterial Detection.

Development of rapid detection strategies that target potentially pathogenic bacteria has gained increasing attention due to the increasing awareness for better health and safety. In this study, we evaluate an intrinsically antimicrobial polymer, 2Gdm, which is a poly(norbornene)-based functional polymer featuring guanidinium groups as side chains, for bacterial detection by the means of triboelectric nanogenerators (TENGs) and triboelectric nanosensors (TENSs). Attachment of bacteria to the sensing layer is anticipated to alter the overall triboelectric properties of the underlying polymer layer. The positively charged guanidinium functional groups can interact with the negatively charged phospholipid bilayer of bacteria and lead to bacterial death, which can then be detected by optical microscopy, X-ray photoelectron microscopy, and more advanced self-powered sensing techniques such as TENGs and TENSs. The double bonds present along the poly(norbornene) backbone allow for thermally induced cross-linking to obtain X-2Gdm and thus rendering materials remain stable in water. By monitoring the change in voltage output after immersion in various concentrations of Gram-negative Escherichia coli (E. coli) and Gram-positive Streptococcus pneumoniae (S. pneumoniae), we have demonstrated the utility of X-2Gdm as a new polymer dielectric for autonomous bacterial detection. As the bacterial concentration increases, the amount of adsorbed bacteria also increases, resulting in a decrease in the surface potential of the X-2Gdm thin film; this reduction in surface potential can cause a decrease in the triboelectric output for both TENGs and TENSs, which serves as a key working mechanism for facile bacterial detection. TENG and TENS systems are capable of detecting E. coli and S. pneumoniae within a range of 4 × 105 to 4 × 108 CFU/mL with a limit of detection of 106 CFU/mL. This report highlights the promising prospects of employing TENGs and TENSs as innovative sensing technologies for rapid bacterial detection by leveraging the electrostatic interactions between bacterial cell membranes and cationic groups present on polymer surfaces.

The 6-item Kessler psychological distress scale to survey serious mental illness among Chinese undergraduates: Psychometric properties and prevalence estimate.

OBJECTIVE: To evaluate the psychometric properties of the 6-item Kessler psychological distress scale (K6) in screening for serious mental illness (SMI) among undergraduates in a major comprehensive university in China. METHOD: The K6 was self-completed by 8289 randomly sampled participants. A group of them (n=222) were re-assessed using K6 and interviewed using the Chinese version of Composite International Diagnostic Interview 3.1 (CIDI-3.1). RESULTS: The test-retest reliability of the K6 scale was 0.79, the Cronbach's alpha was 0.84, and its area under the receiver operating curve (AUC) for diagnosing CIDI-3.1 SMI was 0.85 (95% CI=0.80-0.90). For the optimal cut-off of K6 (12/13), the sensitivity (SEN), specificity (SPE), positive predictive value (PPV), negative predictive value (NPV), and classification accuracy (AC) were 0.83, 0.79, 0.60, 0.93, and 0.80, respectively. The 12-month prevalence of SMI was estimated as 3.97% using this optimal cut-off. Binary logistic regression analysis (including gender, ethnicity, grade, number of siblings and family residency location) showed that only family residency location in rural areas compared to urban areas was significantly associated with more SMI. CONCLUSIONS: This study documented the value of using the K6 for detecting SMI in Chinese undergraduate populations and supported its cross-cultural reliability and validity.